[swift-evolution] [Pitch] Moving where Clauses Out Of Parameter Lists

[Pyry Jahkola]

Joe,

Just from your experience on this topic, is there any reason not to also move the primary constraints into the trailing `where` clause?

So instead of what you wrote, we'd have it this way:

    func foo<T, U>(x: T, y: U) -> Result<T,U>
       where T: Foo, U: Bar, T.Foo == U.Bar /*, etc. */
    {
    }

…as well as:

    struct Foo<T, U>
       where T: Foo, U: Bar, T.Foo == U.Bar
    {
    }

Like I said earlier in this thread, I think this would also make the `extension` syntax more uniform with types (by turning generic parameters into strictly locally visible things):

    extension Foo<T, U> where U == Baz { // (Could've used X and Y here as well.)
        // Now it's clear where the names T and U come from.
        var bazzes: [U] { return ... }
    }

— Pyry

> I think this is a good idea, though I would put the `where` clause after the function signature:
> 
> func foo<T: Foo, U: Bar>(x: T, y: U) -> Result<T,U>
>    where T.Foo == U.Bar /*, etc. */
> {
> }
> 
> As others noted, it's also appealing to do this for type declarations too:
> 
> struct Foo<T: Foo, U: Bar>
>    where T.Foo == U.Bar
> {
> }
> 
> and that gives a consistent feeling with extensions and protocol declarations.


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20160406/4e7010d7/attachment.html>