<div dir="ltr">On Sun, Dec 25, 2016 at 10:18 PM, Daniel Leping <span dir="ltr"><<a href="mailto:daniel@crossroadlabs.xyz" target="_blank">daniel@crossroadlabs.xyz</a>></span> wrote:<br><div class="gmail_extra"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div>Usually it's a generic function that needs to return a value from some other function or a default value (zero) in a case of some conditions. Optional value is an arguable solution in quite some scenarios. Afaik, sometimes it can be used for optional resolution.</div></blockquote><div><br></div><div>Right, I'd agree that Optional is the idiomatic way to do it. Afaict, there's not much you can do with a default value that you couldn't with nil, unless you have some guarantee as to _what_ that default is; however, I'd expect that in every case that you can rely on a guarantee about a default value which would be more useful than nil, it's going to require more specific knowledge of your type than an all-encompassing `DefaultConstructible` can provide.</div><div><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div>Also, generic factories. Widely used in ORM solutions.</div></blockquote><div><br></div><div>Can you elaborate on this? Why is Optional not a solution here?</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div>As mentioned above, algorythmical stuff that requires Zero.</div></blockquote><div><br></div><div>I'm still not convinced there exist credible use cases that need to be generic over both collections and floating point, for instance. In fact, in my experience, there are few math-heavy algorithms where one can ignore even the distinction between integers and binary floating point. By the time you get down to matrix math, you start to run into difficulties that require separate implementations for Float and Double.</div><div><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="HOEnZb"><div class="h5"><div><div class="gmail_quote"><div>On Mon, 26 Dec 2016 at 8:38 Xiaodi Wu <<a href="mailto:xiaodi.wu@gmail.com" target="_blank">xiaodi.wu@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="m_-687985868842093688gmail_msg">Can you give some examples of what you used this approach to do?</div><div class="m_-687985868842093688gmail_msg"><div class="gmail_extra m_-687985868842093688gmail_msg"><br class="m_-687985868842093688gmail_msg"></div><div class="gmail_extra m_-687985868842093688gmail_msg"><br class="m_-687985868842093688gmail_msg"><div class="gmail_quote m_-687985868842093688gmail_msg">On Sun, Dec 25, 2016 at 9:49 PM, Daniel Leping <span class="m_-687985868842093688gmail_msg"><<a href="mailto:daniel@crossroadlabs.xyz" class="m_-687985868842093688gmail_msg" target="_blank">daniel@crossroadlabs.xyz</a>></span> wrote:<br class="m_-687985868842093688gmail_msg"><blockquote class="gmail_quote m_-687985868842093688gmail_msg" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="m_-687985868842093688gmail_msg">+1 to this approach. I remember I had to create it on my own for my projects. Would be nice to have it out of the box.</div><div class="m_-687985868842093688m_-767592733113527348HOEnZb m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348h5 m_-687985868842093688gmail_msg"><div class="m_-687985868842093688gmail_msg"><br class="m_-687985868842093688gmail_msg"><div class="gmail_quote m_-687985868842093688gmail_msg"><div class="m_-687985868842093688gmail_msg">On Mon, 26 Dec 2016 at 8:11 Adam Nemecek via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="m_-687985868842093688gmail_msg" target="_blank">swift-evolution@swift.org</a>> wrote:<br class="m_-687985868842093688gmail_msg"></div><blockquote class="gmail_quote m_-687985868842093688gmail_msg" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">> <span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">Yes, those particular types have initializers that take no arguments. That does not address my question. You merely restated your initial observation that many types in Swift have implemented `init()`.</span></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></span></div></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">Right, it's an empirical argument.</span></div></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div>> <span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">I didn't think the value returned by `init()` was regarded as any sort of zero--or even any sort of "default." In fact, some types in Foundation have a static property called `default` distinct from `init()`.</span><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></span></div></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">Let's not talk about those then. This would not apply to every single type in existence, as I've stated previously.</span></div></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></span></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">> </span><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">It gives you something different every time. How can this be squared with your stated motivation regarding concepts of zero and concepts of equality?</span></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></span></div></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">Due to the fact that it's a resource, not a value. As I've stated above, not all of this applies to types that are more resource-like.</span></div></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">> <span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">Or, it's what you get because that's the most trivial possible string. Quite simply, I do not think the designer of most types that implement `init()` have paused to wonder whether the value that you get is the identity element associated with the most useful and prominent operation that can be performed on that type. I certainly never have.</span><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></span></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">This is an appeal to tradition. </span></div></div></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></span></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">> </span><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">The statement I wrote was in JavaScript, so I'm not sure what you mean by returning an optional. `[]</span><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">.reduce((a, b) => a + b)` results in an error in JavaScript. In Swift, such a function may also be implemented with a precondition that the array is not empty and would not return an optional.</span></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></span></div></div></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">I was talking about their </span><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">analogous </span><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">swift implementations.</span></div></div></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">> <span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">Can you give an example of an algorithm dealing with tensors where you would use a `DefaultConstructible` generic over all types that have `init()`, as opposed to working with the existing `Integer`, `FloatingPoint`, and other numerical protocols?</span></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></span></div></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">If it's implemented as either nested collections or numbers. </span></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></span></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div></div><div class="gmail_extra m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">On Sun, Dec 25, 2016 at 6:00 PM, Xiaodi Wu <span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><<a href="mailto:xiaodi.wu@gmail.com" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" target="_blank">xiaodi.wu@gmail.com</a>></span> wrote:<br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><blockquote class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">On Sun, Dec 25, 2016 at 7:30 PM, Adam Nemecek <span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><<a href="mailto:adamnemecek@gmail.com" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" target="_blank">adamnemecek@gmail.com</a>></span> wrote:<br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></span><div class="gmail_extra m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><blockquote class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail- m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">> Is it well settled, either in Swift or in C++/Rust/etc., that the value returned by a default initializer/constructor is regarded as an identity element or zero? </span><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></span></div></span><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">Int() == 0, String() == "" so to some extent by convention, a lot of types have a default value as is.</span></div></div></blockquote><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div></span><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">Yes, those particular types have initializers that take no arguments. That does not address my question. You merely restated your initial observation that many types in Swift have implemented `init()`.</div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">I didn't think the value returned by `init()` was regarded as any sort of zero--or even any sort of "default." In fact, some types in Foundation have a static property called `default` distinct from `init()`. In Rust, the Default trait requires a function called `default()`, which is documented as being useful when you want "some kind of default value, and don't particularly care what it is."</div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">I was asking whether there's some understanding, of which I've been unaware, that the result of `init()` (or the equivalent in other languages) is expected to be some sort of zero or an identity element. I'm not aware of any evidence to that effect. Are you?</div><span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><blockquote class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail- m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">> Is the thread that I get by writing `let t = Thread()` some kind of zero in any reasonable sense of the word?</span><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></span></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></span></div></span><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">DefaultConstructibility makes less sense for types that represent some sort of resource but make sense for things that are values. But even in this case, Thread() gives you a default value for example if you are working with a resizable collection of threads.</span></div></div></blockquote><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div></span><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">It gives you something different every time. How can this be squared with your stated motivation regarding concepts of zero and concepts of equality?</div><span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><blockquote class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">A better question is why does thread currently implement a default constructor? </span></div></div></blockquote><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div></span><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">It's an initializer that takes no arguments, because none are needed for a new thread. How else would you write it?</div><span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><blockquote class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail- m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">> Do you mean to argue that for an integer the additive identity should be considered "more prominent and useful" than the multiplicative identity? I'm not aware of any mathematical justification for such a conclusion.</div></div><div style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div></span><div style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">I do. The justification is that if I call the default constructor of Int currently, I get the value of 0.</div></div></blockquote><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div></span><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">This is backwards. Why do you believe that the value you obtain from `init()` is intended to be an identity element at all, let alone the most important one? (It's also circular reasoning. Since `init()` only ever gives you one value at a time, by your reasoning it demonstrates that every type must have one "more prominent and useful" identity, which is begging the question.)</div><span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><blockquote class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">Which means that the binary operation must be addition.</div></div></blockquote><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div></span><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">Based on the value of `Int.init()`, you conclude that addition of integers is a "more prominent and useful" operation than multiplication? Again, this is backwards. Rather, we know that each numerical type belongs to multiple ring algebras; there is no basis for reckoning any as "more useful." Since `init()` can only ever give us one value at a time, we know that `init()` cannot give a value that is a meaningful default with respect to any particular operation.</div><span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><blockquote class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">If I call String() I get "" which is the identity of the + String operation.</div></div></blockquote><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div></span><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">Or, it's what you get because that's the most trivial possible string. Quite simply, I do not think the designer of most types that implement `init()` have paused to wonder whether the value that you get is the identity element associated with the most useful and prominent operation that can be performed on that type. I certainly never have.</div><span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><blockquote class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail- m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">> <span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">Going to your original example, I should add: other languages provide a version of `reduce` that doesn't require an initial result (for instance, JavaScript). In JavaScript, `[1, 2, 3].reduce((a, b) => a + b)` uses the element at array index 0 as the initial result, and the accumulator function is invoked starting with the element at array index 1. This is precisely equivalent to having `reduce` use the additive identity as the default initial result when + is the accumulator function and the multiplicative identity when * is the accumulator function (with the accumulator function being invoked starting with the element at array index 0). It does not require a DefaultConstructible protocol. What more ergonomic solution could be implemented using a monoidic wrapper type?</span></div><div style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></span></div></span><div style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">These two will have different signatures. The reduce you describe returns an optional,</div></div></blockquote><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div></span><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">The statement I wrote was in JavaScript, so I'm not sure what you mean by returning an optional. `[]<span style="font-size:12.800000190734863px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">.reduce((a, b) => a + b)` results in an error in JavaScript. In Swift, such a function may also be implemented with a precondition that the array is not empty and would not return an optional.</span></div><span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><blockquote class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">the other one would returns the default value.</div></div></blockquote><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div></span><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">In what scenario would you prefer to propagate a default after reducing a potential empty collection _without supplying an explicit default_ for that operation? This would certainly violate the Swift convention of not defaulting to zero and, I suspect, most users of Swift would not regard that as ergonomic at all.</div><span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"> </div><blockquote class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">Fundamentally the default constructibles are useful in numerical computations e..g. dealing with tensors.</div></div></blockquote><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div></span><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">Can you give an example of an algorithm dealing with tensors where you would use a `DefaultConstructible` generic over all types that have `init()`, as opposed to working with the existing `Integer`, `FloatingPoint`, and other numerical protocols? (I should also add, FWIW, I have never seen a generic algorithm written for integers or FP types that has preferred the use of `T()` over `0`.)</div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809h5 m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><blockquote class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-HOEnZb m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-h5 m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="gmail_extra m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">On Sun, Dec 25, 2016 at 3:30 PM, Xiaodi Wu <span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><<a href="mailto:xiaodi.wu@gmail.com" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" target="_blank">xiaodi.wu@gmail.com</a>></span> wrote:<br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><blockquote class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">On Sun, Dec 25, 2016 at 5:27 PM, Adam Nemecek <span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><<a href="mailto:adamnemecek@gmail.com" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" target="_blank">adamnemecek@gmail.com</a>></span> wrote:<br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></span><div class="gmail_extra m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><blockquote class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail- m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">> <span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">*Which* APIs become more ergonomic?</span></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></span></div></span><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">I'll get back to this question in a second if I may. This would be a longer discussion and I first want to make sure that before we get into the details that there is a possibility of this being introduced (I'm asking if violating the no zero defaults is more important than slightly more ergonomic APIs). But to give a broad answer I think that the concept of a zero is closely related to the concept of equality (and all the things that build up on equality such as comparability and negation). </div><span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail- m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">> <span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">1) How does this square with Swift’s general philosophy to not default initialize values to “zero”?</span></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></span></div></span><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">I actually wasn't aware of this philosophy. Despite this philosophy, look at how many types actually currently implement a default constructor.</span></div></div></blockquote><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div></span><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">(Not a rhetorical question:) Is it well settled, either in Swift or in C++/Rust/etc., that the value returned by a default initializer/constructor is regarded as an identity element or zero? Is the thread that I get by writing `let t = Thread()` some kind of zero in any reasonable sense of the word?</div><span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"> </div><blockquote class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">Also can I ask what's the motivation behind this philosophy? </span></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">I think that in Swift, default constructibility makes complete sense for (most?) structs, maybe less so for classes. </span></div><span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail- m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div>> <span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">2) To your original example, it isn’t immediately clear to me that reduce should choose a default identity. Some types (e.g. integers and FP) belong to multiple different ring algebras, and therefore have different identity values that correspond to the relevant binary operations.</span><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></span></div></span><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="font-size:12.8px" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">This is a good point that I've considered as well but felt that for the most part, there is one particular identity and associated operation that is more prominent and useful than others. Furthermore, modeling different algebras isn't mutually exclusive with writing generic algorithms that rely on this protocol, you can always introduce some monoidic wrapper type that defines the more appropriate default value and operation.</span></div></div></blockquote><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div></span><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">Do you mean to argue that for an integer the additive identity should be considered "more prominent and useful" than the multiplicative identity? I'm not aware of any mathematical justification for such a conclusion.</div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">Going to your original example, I should add: other languages provide a version of `reduce` that doesn't require an initial result (for instance, JavaScript). In JavaScript, `[1, 2, 3].reduce((a, b) => a + b)` uses the element at array index 0 as the initial result, and the accumulator function is invoked starting with the element at array index 1. This is precisely equivalent to having `reduce` use the additive identity as the default initial result when + is the accumulator function and the multiplicative identity when * is the accumulator function (with the accumulator function being invoked starting with the element at array index 0). It does not require a DefaultConstructible protocol. What more ergonomic solution could be implemented using a monoidic wrapper type?</div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376h5 m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div></div><blockquote class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-HOEnZb m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-h5 m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="gmail_extra m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">On Sun, Dec 25, 2016 at 1:24 PM, Chris Lattner <span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><<a href="mailto:clattner@apple.com" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" target="_blank">clattner@apple.com</a>></span> wrote:<br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><blockquote class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div style="word-wrap:break-word" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">On Dec 25, 2016, at 12:54 PM, Adam Nemecek via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" target="_blank">swift-evolution@swift.org</a>> wrote:</span><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><blockquote type="cite" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">Does enabling a lot of small improvements that make APIs more ergonomic count as practical?</div></div></blockquote><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div></span><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">Yes, that would count as practical, but Xiaodi’s question is just as important. *Which* APIs become more ergonomic?</div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">Here are a couple of more questions:</div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">1) How does this square with Swift’s general philosophy to not default initialize values to “zero”?</div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">2) To your original example, it isn’t immediately clear to me that reduce should choose a default identity. Some types (e.g. integers and FP) belong to multiple different ring algebras, and therefore have different identity values that correspond to the relevant binary operations.</div><span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596HOEnZb m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><font color="#888888" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">-Chris</div></font></span><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596h5 m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><blockquote type="cite" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="gmail_extra m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">On Sun, Dec 25, 2016 at 12:19 PM, Xiaodi Wu <span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><<a href="mailto:xiaodi.wu@gmail.com" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" target="_blank">xiaodi.wu@gmail.com</a>></span> wrote:<br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><blockquote class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">On Sun, Dec 25, 2016 at 3:07 PM, Adam Nemecek <span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><<a href="mailto:adamnemecek@gmail.com" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" target="_blank">adamnemecek@gmail.com</a>></span> wrote:<br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></span><div class="gmail_extra m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><blockquote class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">There's a book that provides quite a bit of info on this <div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><a href="https://smile.amazon.com/Elements-Programming-Alexander-Stepanov/dp/032163537X?sa-no-redirect=1" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" target="_blank">https://smile.amazon.com/<wbr>Elements-Programming-<wbr>Alexander-Stepanov/dp/<wbr>032163537X?sa-no-redirect=1</a><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">They say that DefaultConstructible is one of the essential protocols on which most algorithms rely in one way or another. One of the authors is the designer of the C++ STL and basically the father of modern generics.</div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">This protocol is important for any algebraic structure that deals with the concept of appending or addition (as "zero" is one of the requirements of monoid). There isn't a good short answer to your question. It's a building block of algorithms. Think about why a RangeReplaceableCollection can provide you with a default constructor but a Collection can't. </div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="color:rgb(80,0,80)" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></span></div></div></blockquote><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div></span><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">It's well and fine that most algorithms rely on the concept in one way or another. Yet the Swift standard library already implements many generic algorithms but has no DefaultConstructible, presumably because there are other protocols that guarantee `init()` and the algorithms being implemented don't need to be (practically speaking) generic over all DefaultConstructible types. My question is: what practical use cases are there for an explicit DefaultConstructible that are impractical today?</div><span class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><blockquote class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><span style="color:rgb(80,0,80)" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">On Sun, Dec 25, 2016 at 11:37 AM, Xiaodi Wu </span><span style="color:rgb(80,0,80)" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><<a href="mailto:xiaodi.wu@gmail.com" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" target="_blank">xiaodi.wu@gmail.com</a>></span><span style="color:rgb(80,0,80)" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"> wrote:</span><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289HOEnZb m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289h5 m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="gmail_extra m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><blockquote class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">Can you give some other examples of generic algorithms that would make use of this DefaultConstructible? I'm having trouble coming up with any other than reduce.<br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951h5 m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">On Sun, Dec 25, 2016 at 14:23 Adam Nemecek via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" target="_blank">swift-evolution@swift.org</a>> wrote:<br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div></div></div><blockquote class="gmail_quote m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951h5 m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">This protocol is present in C++ <a href="http://en.cppreference.com/w/cpp/concept/DefaultConstructible" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" target="_blank">http://en.cppreference.<wbr>com/w/cpp/concept/<wbr>DefaultConstructible</a> as well as in Rust <a href="https://doc.rust-lang.org/std/default/" class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg" target="_blank">https://doc.rust-lang.org/std/<wbr>default/</a><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">It's the identity element/unit of a monoid or a zero.<br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">The Swift implementation is very simple (I'm open to different names)<br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">protocol DefaultConstructible {</div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"> init() </div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">}</div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">A lot of the standard types could then be made to conform to this protocol. These include all the numeric types, collection types (array, set, dict), string, basically at least every type that currently has a constructor without any arguments.</div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">The RangeReplaceableCollection protocol would inherit from this protocol as well. <br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">This protocol would simplify a lot of generic algorithms where you need the concept of a zero (which shows up a lot)</div></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg">Once introduced, Sequence could define an alternative implementation of reduce where the initial result doesn't need to be provided as it can be default constructed.</div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><div class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359m_3012462067322088809m_1176161565890972384gmail-m_2687622816934730376m_-5821329404718624302gmail-m_3993794689939404596m_-267952324834337685m_8912025549324475289m_699475458640075951m_-6015751673947924360gmail_msg m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div></div></div></div></div><br class="m_-687985868842093688gmail_msg"><br class="m_-687985868842093688gmail_msg">______________________________<wbr>_________________<br 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class="m_-687985868842093688gmail_msg"></blockquote></div><br class="m_-687985868842093688gmail_msg"><br class="m_-687985868842093688gmail_msg"></blockquote></div><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><br class="m_-687985868842093688gmail_msg"><br class="m_-687985868842093688gmail_msg"></div></div></blockquote></span></div><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div></div><br class="m_-687985868842093688gmail_msg"><br class="m_-687985868842093688gmail_msg"></blockquote></div><br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg m_-687985868842093688gmail_msg"></div><br class="m_-687985868842093688gmail_msg"><br class="m_-687985868842093688gmail_msg">______________________________<wbr>_________________<br class="m_-687985868842093688m_-767592733113527348m_4453439987323397359gmail_msg 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