[swift-evolution] [proposal] Generic type aliases

Joe Groff jgroff at apple.com
Wed Mar 16 22:32:49 CDT 2016

> On Mar 16, 2016, at 5:02 PM, Chris Lattner <clattner at apple.com> wrote:
> On Mar 16, 2016, at 4:56 PM, Joe Groff <jgroff at apple.com <mailto:jgroff at apple.com>> wrote:
>>> We shouldn’t infer it the requirement.
>>> Rationale: I see this as analogous (in two ways) to why we don’t infer hashability of T in:
>>> func f<T>(…) {
>>>   let x : Dictionary<T, String>
>>> }
>> However, we do infer the `T: Hashable` in a case like this:
>> func foo<T>(x: Dictionary<T, String>) {}
>> `typealias` feels similar to that to me. It doesn't have to be a global analysis, just an analysis of the RHS of the typealias.
> I consider the RHS of the typealias to be the “body” of the type alias, and parameters to be part of the “signature” of the funcdecl.

I'm OK starting with the base design that constraints have to be explicit. My gut tells me though that `typealias` is close enough syntactically to `var` that many people will expect the inference to occur, but we can always add it later.

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