[swift-evolution] /*Let it be*/ func() -> @discardable Bool {} /*Rather Than*/ @discardableResult func() -> Bool {}

[Mike Kluev]

On 13 October 2017 at 22:50, Jean-Daniel <mailing at xenonium.com> wrote:

I mean:
>
> func foo() -> Int { … }
>
> func bar(callback: () -> discardable Int) { … }
>
> bar(foo) // does it warns ?
> bar({ 3 }) // does it warns ? If it does, how to avoid it ?
>

thanks.

>>> And allowing it in signature but not in lambda would be confusing.

not any more confusing than it is now (allowing @discardableResult before
function name and not allowing it before closure parameters).

but, if to fix that, than could be this (orthogonal to whether it is
"@discardableResult" or "discardable"):

func foo() -> Int {}
func bar(_ callback: () -> discardable Int) {}

bar(foo) // error, type mismatch
bar({ 3 }) // error, type mismatch
bar({ () -> discardable Int in 3 }) // ok, types matched

- and -

func poo() -> discardable Int {}
func baz(_ callback: () -> Int) {}

baz(poo) // ok, types compatible
baz({ 3 }) // ok, types matched
baz({ () -> discardable Int in 3 }) // ok, types compatible

Mike
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20171013/be888c55/attachment.html>