[swift-evolution] I think we need more to our type calculus

[Xiaodi Wu]

type(of:) is the Swift 3 spelling of what was known in Swift 2 as
dynamicType.
On Wed, Feb 8, 2017 at 14:09 Daryle Walker via swift-evolution <
swift-evolution at swift.org> wrote:

> 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.
>
> 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.
>
> Some queries/requests:
>
> 1. Is the expression within “type(of:)” evaluated?
> 2. I think we need the equivalent of "std::declval” from C++. Especially
> if the answer to (1) is yes.
> 3. Why isn’t the return type(?) of “type(of:)” compile-time enough to be
> used as a type-alias?
> 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?
>
> —
> Daryle Walker
> Mac, Internet, and Video Game Junkie
> darylew AT mac DOT com
>
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