While I know it might be a bit strange to have different rules for each side, I
think I prefer empty brackets on the left and Void on the right, but in
combination with required parenthesis on the left. So we’d have:
() -> Void // yes
Void -> () // no
() -> () // no (rhs interpreted as empty tuple which is
not allowed)
() -> Int // yes
Int -> Void // no (lhs no parens)
(Int) -> Void // yes
I think the parenthesis helps to highlight that it’s a function/closure, I
think it’s also clearer for cases like:
((Int, String)) -> Void // this is a closure taking a two-part tuple
(Int, String) -> Void // this is definitely a closure taking
an Int and a String
> On 23 Apr 2016, at 11:47, Антон Жилин via swift-evolution
> <[email protected]> wrote:
>
> Therefore the impermissible:
> (()) -> () Is identical to:
> (Void) -> () So to follow these rules, it must instead be:
> Void -> () … and we’re back to T1 -> T2 : )
>
> Wrong! If we enforce parentheses in function types, we won't be able to write
> Void -> ()
> Parentheses will be required on the grammar level. The correct way to write
> this will be:
> () -> () or () -> Void
> The following will be legal:
> (Void) -> () and (()) -> ()
> It is a function that takes a single parameter () and returns ().
> I additionally propose that the following should be illegal, because
> additional parentheses aren't needed there:
> ((())) -> () and () -> (()) and just (Int) and (())
> Hope it cleared up things a little bit.
> - Anton
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