<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 Feb 8, 2017, at 12:09 PM, Daryle Walker 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=""><div class="">I’ve been trying to get the maximum of a list of counts. I started by using “myCollection.map { $0.myCountProperty }.reduce(0, max)”. Then I thought I should really use the value closest to negative infinity as the base. The problem is how to get that value. The current hard-coded “0” works because the count type ultimately aliases “Int”, but shouldn’t have to count on that. I put in “MyCountType.min”, where “MyCountType” is hard coded from the docs of “myCountProperty”, but I shouldn’t have to do that either.</div><div class=""><br class=""></div><div class="">There is a “type(of:)” global function, which I did use. But not only did I have to make up an expression to go in there, its return value, some sort of meta-type stuff I don’t understand, can’t be used on the right side of a “typealias” construct. I ultimately used “let lowestCount = type(of: anElement.myCountProperty).min” to get what I needed.</div><div class=""><br class=""></div><div class="">Some queries/requests:</div><div class=""><br class=""></div><div class="">1. Is the expression within “type(of:)” evaluated?</div></div></div></blockquote><div><br class=""></div>Yes. Eg,</div><div><br class=""></div><div>class Base {}</div><div>class Derived : Base {}</div><div><br class=""></div><div>func foo() -> Base { return Derived() }</div><div><br class=""></div><div>type(of: foo()) // this is Derived.self, not Base.self</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="">2. I think we need the equivalent of "std::declval” from C++. Especially if the answer to (1) is yes.</div><div class="">3. Why isn’t the return type(?) of “type(of:)” compile-time enough to be used as a type-alias?</div></div></div></blockquote><div><br class=""></div><div>type(of:) is not a real function because it’s return type depends on the input type in a funny way. If the input type T is an existential, then type(of:) returns an existential metatype; otherwise, it returns a concrete metatype. So it’s almost as if the signature is (T) -> (T.Type), but not quite.</div><div><br class=""></div><div>Slava</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="">4. Should we add something like the C++ type-traits collection of generic structures to give use type information as type-aliases or type-level instances?</div><div class=""><br class=""></div><div class="">
<div style="letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">— </div><div class="">Daryle Walker<br class="">Mac, Internet, and Video Game Junkie<br class="">darylew AT mac DOT com </div></div>
</div>
<br class=""></div>_______________________________________________<br class="">swift-evolution mailing list<br class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a><br class="">https://lists.swift.org/mailman/listinfo/swift-evolution<br class=""></div></blockquote></div><br class=""></body></html>