<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=""><div><blockquote type="cite" class=""><div class="">On Sep 9, 2017, at 10:31 PM, Chris Lattner 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=""><div 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="">- I’d love to see several of the most common random kinds supported, and I agree it would be nice (but not required IMO) for the default to be cryptographically secure.</div></div></blockquote><div><br class=""></div><div><div>I would be very careful about choosing a "simple" solution. There is a log, sad history of languages trying to provide a "simple" random number generator and accidentally providing a powerful footgun instead. But:</div></div><br class=""><blockquote type="cite" class=""><div class=""><div class="" 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;">- We should avoid the temptation to nuke this mosquito with a heavy handed solution designed to solve all of the world’s problems: For example, the C++ random number stuff is crazily over-general. The stdlib should aim to solve (e.g.) the top 3 most common cases, and let a more specialized external library solve the fully general problem (e.g. seed management, every distribution imaginable, etc).</div></div></blockquote></div><div><br class=""></div><div>That's not to say we need to have seven engines and twenty distributions like C++ does. The standard library is not a statistics package; it exists to provide basic abstractions and fundamental functionality. I don't think it should worry itself with distributions at all. I think it needs to provide:</div><div><br class=""></div><div><span class="Apple-tab-span" style="white-space:pre"> </span>1. The abstraction used to plug in different random number generators (i.e. an RNG protocol of some kind).</div><div><br class=""></div><div><span class="Apple-tab-span" style="white-space:pre"> </span>2. APIs on existing standard library types which perform basic randomness-related functions correctly—essentially, encapsulating Knuth. (Specifically, I think selecting a random element from a collection (which also covers generating a random integer in a range), shuffling a mutable collection, and generating a random float will do the trick.)</div><div><br class=""></div><div><span class="Apple-tab-span" style="white-space:pre"> </span>3. A default RNG with a conservative design that will sometimes be too slow, but will never be insufficiently random.</div><div><br class=""></div><div>If you want to pick elements with a Poisson distribution, go get a statistics framework; if you want repeatable random numbers for testing, use a seedable PRNG from XCTest or some other test tools package. These can leverage the standard library's RNG protocol to work with existing random number generators or random number consumers.</div><div><br class=""></div><div class="">
<span class="Apple-style-span" style="border-collapse: separate; font-variant-ligatures: normal; font-variant-east-asian: normal; font-variant-position: normal; line-height: normal; border-spacing: 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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