<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div><blockquote type="cite" class=""><div class="">On Jan 9, 2018, at 4:12 AM, Jonathan Hull <<a href="mailto:jhull@gbis.com" class="">jhull@gbis.com</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="">Some thoughts:<div class=""><br class=""></div><div class="">- How do I randomly select an enum?<br class=""></div></div></div></blockquote><div><br class=""></div><div>Vote for SE-0194! :)</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=""><div class="">- I like that RandomNumberGenerator doesn’t have an associated type. I agree that we should just spit out UInt64s for simplicity.</div></div></div></div></blockquote><div><br class=""></div><div>It simplifies things a lot, at some performance cost. For example, the LCRNG type really produces UInt32s, so I have to use two of its outputs to generate one value, even if I don’t need that many bits.</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=""><div class="">- I don’t like how it is so closely tied with Range. I realize that both Int and Float work with Ranges, but other random types do not (e.g. CGVectors). You are special casing FixedWidthInteger and BinaryFloatingPoint, which are very important… but we lose the ability to deal with other randomly generated types.</div><div class=""><br class=""></div><div class="">- Following on the previous point, I don’t like that the code for dealing with Integers/Floats is in Range. It feels like things aren’t properly encapsulated. </div></div></div></div></blockquote><div><br class=""></div><div>I actually agree with you, and for getting individual values prefer the form `let x = Int.random(in: 1…10)`. Here’s how I got to what’s in the playground:</div><div><br class=""></div><div>1) We definitely want to be able to select a random element from a collection.</div><div>2) Given that, we’ll have (1…10).random() and (0..<10).random() even if those aren’t what we prefer, and people will use them.</div><div>3) If people use that construction for integers, it will be strange to not have the same facility for floating-point numbers.</div><div>4) Once we have the range-based capability for both, the type-based versions are redundant (i.e., they can be added in the future if we decide we made the wrong decision by excluding them).</div><div><br class=""></div><div>You’re of course correct that a pattern of range-based random functions doesn’t extend well to other types. I show on the last page a couple different ways of writing those, for Bool and Data. Most of the other types you’d want to create lie outside the Swift standard library, so we can’t address really those here.</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=""><div class="">- Why bother supporting non-closed Ranges at all? If you only allow closed ranges, then you can’t end up with an empty range. The only difference in behavior I can think of is on floating point, but I can’t think of a use-case where excluding the supremum is actually useful in any real world way.</div></div></div></div></blockquote><div><br class=""></div><div>Half-open ranges are a major use case for generating random numbers, particularly when working with collections. Whenever you see that someone’s written `random() % n`, that’s the half-open range 0..<n.</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=""><div class="">- This may sound strange, but I would <i class="">really</i> like to see Bool handled as a default implementation on the generator protocol itself. On my own version of this I have both the ‘coinFlip()’ and ‘oneIn(_ num:Int)’ methods which I find extremely useful. CoinFlip just gives you a random bool, whereas you can say things like oneIn(100) to get ‘true’ roughly 1 out of every 100 times you call it. These are useful for branching randomly. They are most useful on the source/generator itself because it is ergonomic when you need to rewind the source.</div></div></div></div></blockquote><div><br class=""></div><div>Bool is certainly a very important type to be able to randomly generate. I’m not opposed to it being included in a proposal, but it’s simple enough to do on your own that it didn’t pass the “minimal” test that I was using in the playground. You could use something like this static method:</div><div><br class=""></div><div><div><div> extension Bool {</div><div> static func random(</div><div> probability: Double = 0.5, </div><div> using generator: RandomNumberGenerator = Random.default</div><div> ) {</div><div> return (0.0 ..< 1.0).random(using: generator) < probability</div><div> }</div><div> }</div><div><br class=""></div><div>I don’t think there should be any value-producing methods on generators—most users shouldn’t need to think about generators at all, and the ones who have a specific need (repeatability, rewinding, etc) should be able to use the same APIs as the people who aren’t thinking about them.</div><div><br class=""></div></div></div><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=""><div class="">- IMO distributions should be sources/generators themselves which just wrap another source. We could have a subprotocol of RandomNumberGenerator which just semantically guarantees uniform distribution, and then distributions that need it could be sure of the input distribution. Notice this doesn’t limit the distribution to only be used for Integers as they are in the demo. They can be used anywhere a source can be used.</div></div></div></div></blockquote><div><br class=""></div><div>I’d really like to maintain a clear line between generators and distributions (which I don’t think we need an additional protocol for). Distributions create values of a specific kind of type, with a particular distribution, which usually isn't suitable to use as the input for another algorithm that needs random data. Generators just pump out (hopefully) uniformly distributed bits, which distributions and other algorithms can then interpret and shape.</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=""><div class="">- Having a subprotocol for generators which can be rewound is extremely important for entire classes of real-world problems. I have spent a lot of time using this and it solves a LOT of problems. For example, I have a Lorem Ipsum Generator which takes Attributes and a CGSize to fill. It works by branching (using the Bool methods above) and then rewinding bits which don’t fit (If you just futz with the last part instead of generating appropriate clauses, it won’t look right). I also have a bunch of backtracking algorithms which rely on this rewind ability. Plus numerous visual effects which rely on a repeatable rewindable source.</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span><i class="">- Tl;dr: It isn’t enough to just have a seed, you need to be able to mark a state of a generator and return to that state later.</i></div><div class=""><br class=""></div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>My RepeatableRandomSource Protocol has 3 extra methods:</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>- It takes a seed</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>- It has a mark() method which returns a token</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>- It has a returnToMark(_ mark:Mark) method which takes a token and restores the appropriate state </div></div></div></div></blockquote><div><br class=""></div><div>That’s neat, I’ve never used a generator like this! The RandomNumberGenerator protocol would certainly allow for a generator with these features, and libraries or future additions to the standard library could include that kind of protocol.</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=""><div class="">- I really appreciate that you made a playground :-)</div></div></div></div></blockquote><div><br class=""></div><div>Thanks!</div><div><br class=""></div><div>Nate</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=""><div class="">Thanks,</div><div class="">Jon</div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><div class=""><div class=""><div class=""><blockquote type="cite" class=""><div class="">On Jan 8, 2018, at 11:02 AM, Nate Cook 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; line-break: after-white-space;" class="">I created a playground to explore this question, starting with a minimal subset of the proposal’s additions and building from there. The attached playground demonstrates what’s possible with this subset on the first page, then uses subsequent pages to explore how the main random facilities of the C++ STL work under this model. (In my opinion, they work pretty well!)<div class=""><br class=""></div><div class="">The subset in the playground has three main differences from the proposal:</div><div class=""> - It doesn't include a <font face="Menlo" class="">Randomizable</font> protocol or a <font face="Menlo" class="">random</font> property on numeric types.<br class=""> - It doesn't include the static <font face="Menlo" class="">random(in:)</font> methods on numeric types, either.<br class=""> - The <font face="Menlo" class="">RandomNumberGenerator</font> protocol doesn't have an associated type. Instead, it requires all conforming types to produce <font face="Menlo" class="">UInt64</font> values.<br class=""><br class=""></div><div class="">I’ve tried to include a bit of real-world usage in the playground to demonstrate what writing code would look like with these additions. Please take a look!</div><div class=""><br class=""></div><div class="">Nate</div><div class=""><br class=""></div><div class=""></div></div><span id="cid:ABC18921-24CA-48D8-BC24-C1F445F8C252@hsd1.ca.comcast.net." class=""><Random.playground.zip></span><meta http-equiv="Content-Type" content="text/html; charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class=""></div><div class=""><br class=""></div><div class=""><div class=""><blockquote type="cite" class=""><div class="">On Dec 2, 2017, at 9:50 PM, Dave Abrahams 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="">I don’t have much to say about this other than that I think the discussion seems way too narrow, focusing on spelling rather than on functionality and composability. I consider the “generic random number library” design to be a mostly-solved problem, in <span style="background-color: rgba(255, 255, 255, 0);" class="">the C++ standard library (<a href="http://en.cppreference.com/w/cpp/numeric/random" class="">http://en.cppreference.com/w/cpp/numeric/random</a>). </span>Whatever goes into the Swift standard library does not need to have all those features right away, but should support being extended into something having the same general shape. IMO the right design strategy is to <u class="">implement and use</u> a Swift version of C++’s facilities and only then consider proposing [perhaps a subset of] that design for standardization in Swift.<div class=""><div class=""><br class=""></div><div class="">Sent from my iPad<div class=""><br class="">On Dec 2, 2017, at 5:12 PM, Kyle Murray 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=""><br class=""><div class=""><blockquote type="cite" class=""><div class="">On Dec 2, 2017, at 6:02 PM, Xiaodi Wu 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="">Instead, we ought to make clear to users both the features and the limitations of this API, to encourage use where suitable and to discourage use where unsuitable.</span></div></blockquote></div><br class=""><div class="">I like that you're considering the balance here. I've been lightly following this thread and want to add my thoughts on keeping crypto and pseudorandomness out of the name of at least one <font face="Menlo" class="">random</font> API intended for general use.</div><div class=""><br class=""></div><div class="">For someone who doesn't know or care about the subtleties of insecure or pseudorandom numbers, I'm not sure that the name <font face="Menlo" class="">insecureRandom</font> is effectively much different than <font face="Menlo" class="">badRandom</font>, at least in terms of the information it conveys to non-experts. To Greg's point, that's the opposite of the signal that the API name should suggest because it's what most people should use most of the time. As you say, this API is being designed for general use.</div><div class=""><br class=""></div><div class="">There's a cost to adding extra complexity to names, too. I don't think it's far-fetched to suspect that people who find <font face="Menlo" class="">insecureRandom</font> in an autocomplete listing or search will think "Where's the plain random function?"... and then go looking for a community extension that will inevitably provide a trivial alias: <font face="Menlo" class="">func random() { return insecureRandom() }</font>. That's the sort of adoption I'd expect from something for new programmers, like Swift Playgrounds. Someone's introduction to randomness in programming should probably involve no more than a straightforward mapping from the elementary definition, rather than forcing a teaching moment from more advanced math.</div><div class=""><br class=""></div><div class="">I think there are better places for caveat information than in the API names themselves; documentation being one clear destination. This is in contrast with <font face="Menlo" class="">Unsafe*Pointer</font>, where the safety element is critical enough to be elevated to be more than caveat-level information. You can go really far and create really cool things before these caveats start to apply. Using randomness as a black box in an intro programming environment seems like a much more common scenario than someone attempting to roll their first crypto by only reading API names and hoping for the best.</div><div class=""><br class=""></div><div class="">-Kyle</div></div></blockquote><blockquote type="cite" class=""><div class=""><span class="">_______________________________________________</span><br class=""><span class="">swift-evolution mailing list</span><br class=""><span class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a></span><br class=""><span class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a></span><br class=""></div></blockquote></div></div></div>_______________________________________________<br class="">swift-evolution mailing list<br class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a><br class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br class=""></div></blockquote></div><br class=""></div></div>_______________________________________________<br class="">swift-evolution mailing list<br class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a><br class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br class=""></div></blockquote></div><br class=""></div></div></div></div></div></div></blockquote></div><br class=""></body></html>