<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Apr 9, 2017, at 3:01 PM, Jon Shier via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><span class="Apple-tab-span" style="white-space:pre"> </span>I generally dislike any language change desired because it makes the compiler implementation easier. We saw a few such changes for Swift 3 and all of them were net negatives for the actual users of the language (to a minor extent for most, to be fair).</div></div></blockquote><div><br class=""></div><div>I’m going to have to call shenanigans on this claim :-) At least I can’t _think_ of any Swift 3 features that were designed with the goal of making the implementation simpler. Even the feature removals, such as nuking the ‘function currying’ syntax, took time to implement (and this is not even fully removed yet).</div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""> I would hope that, as the compiler matures, these types of inference performance issues will become less of a problem. Removing a rather nice language feature, especially one that plays such a big role in the “feel” of the language, for short term gain seems rather shortsighted to me.</div></div></blockquote><div><br class=""></div>I agree. The type checker might have pathological behavior in some cases now, but we hope to fix those over time, and none of it is specific to the expressions people usually write in stored property initializers.</div><div><br class=""></div><div>Slava</div><div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><br class=""></div><div class="">Jon Shier<br class=""><div class=""><br class=""></div><div class=""><br class=""><div class=""><blockquote type="cite" class=""><div class="">On Apr 9, 2017, at 11:23 AM, Lucas Neiva via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="content-type" content="text/html; charset=utf-8" class=""><div dir="auto" class=""><div class=""></div><div class="">If inference only works in simple cases, I think it would seem like it works unpredictability to anyone unfamiliar with the implementation details.</div><div class=""><br class=""></div><div class="">I image the question of "why do I have to declare a type here, but not in this case?" coming up.</div><div class=""><br class=""></div><div class="">Declaring types is one of the first things you have to learn anyway. Just declaring a function already requires some understanding of types. Properties are not much different IMO.</div><div class=""><br class="">On 8 Apr 2017, at 08:34, Brent Royal-Gordon via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""><br class=""></div><blockquote type="cite" class=""><div class=""><meta http-equiv="Content-Type" content="text/html charset=us-ascii" class=""><div class=""><blockquote type="cite" class=""><div class="">On Apr 7, 2017, at 12:21 AM, Daniel Duan via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">The cons for doing this are obvious too: the inference makes the language feels more friendly and is, undoubtedly, a beloved feature for many. This would be a source breaking change.</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""></div></blockquote></div><div class=""><br class=""></div><div class="">Beyond just being more friendly, I think it could be considered a teaching issue. A great way to introduce beginners to custom types would be something like:</div><div class=""><br class=""></div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>struct Point {</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>var x = 0.0</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>var y = 0.0</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>}</div><div class=""><br class=""></div><div class="">Or:</div><div class=""><br class=""></div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>struct Person {</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>var name = ""</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>var age = 18</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>}</div><div class=""><br class=""></div><div class="">If you have to explicitly specify types for the properties, that's another thing you need to introduce to people before you can do this.</div><div class=""><br class=""></div><div class="">On the other hand, a very limited form of inference might be fine here. Imagine if we did a sort of limited, single-pass, top-down inference which only understood a few things (literals, tuple syntax, initializer calls), stopped once it had seen enough to infer a complete type, and rejected an expression if it encountered something it didn't understand before finishing. That would probably cover most simple cases, and it would probably only allow expressions whose types were obvious enough that we could use it for arguments, too. (But of course it would mean more code in the compiler, so it might not be worth it.)</div><br class=""><div class="">
<span class="Apple-style-span" style="border-collapse: separate; font-family: Helvetica; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-variant-east-asian: normal; font-variant-position: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; border-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-stroke-width: 0px;"><div class=""><div style="font-size: 12px; " class="">-- </div><div style="font-size: 12px; " class="">Brent Royal-Gordon</div><div style="font-size: 12px; " class="">Architechies</div></div></span>
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