[swift-evolution] [pitch] Eliminate the "T1 -> T2" syntax, require "(T1) -> T2"

[Dave Abrahams]

on Thu Apr 14 2016, Chris Lattner <swift-evolution at swift.org> wrote:

> We currently accept function type syntax without parentheses, like:
>
>   Int -> Float
>   String -> ()
>
> etc.  The original rationale aligned with the fact that we wanted to
> treat all functions as taking a single parameter (which was often of
> tuple type) and producing a tuple value (which was sometimes a tuple,
> in the case of void and multiple return values).  However, we’ve long
> since moved on from that early design point: there are a number of
> things that you can only do in a parameter list now (varargs, default
> args, etc), implicit tuple splat has been removed, and the compiler
> has long ago stopped modeling function parameters this way.  Beyond
> that, it eliminates one potential style war.
>
> Given all this, I think it makes sense to go for syntactic uniformity
> between parameter list and function types, and just require
> parenthesis on the argument list.  The types above can be trivially
> written as:
>
>   (Int) -> Float
>   (String) -> ()
>
> Thoughts?

+1, as I've always said.

By everyone but the purely-functional-programming crowd, ()s are
associated with functions; it makes sense to see them in the type, and
the non-uniformity created by seeing A->B in the places it's allowed is
not balanced by a widespread drop in syntactic noise.

-- 
Dave