[swift-evolution] rethrows as first-class type annotation

[Alexandre Lopoukhine]

Hi Dmitri,

This is a better example than any that I have come up with so far as to why “rethrows” should be a part of the signature. You shouldn’t have to use “try!” to apply a non-throwing function, like {print($0)} to “forEach”.

— Sasha


> On 20 Dec 2015, at 13:37, Dmitri Gribenko <gribozavr at gmail.com> wrote:
> 
> Hi Alexandre,
> 
> I think for this use case we don't actually need 'rethrows' to become
> a part of the closure type, we just need the compiler to allow and
> "instantiate" it in more places.
> 
> The case where we would need 'rethrows' to become a first class part
> of the type system is if we wanted 'rethrows' to be a part of the
> signature of the closure itself, for example:
> 
> (swift) let forEach = [ 10, 20, 30 ].forEach
> // forEach : (@noescape (Int) throws -> Void) throws -> () = (Function)
> 
> Here, a more precise type would be (@noescape (Int) throws -> Void)
> rethrows -> Void.
> 
> Dmitri
> 
> -- 
> main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
> (j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr at gmail.com>*/