+1
Sent from my iPhone
> On May 16, 2016, at 4:06 PM, Joe Groff via swift-evolution
> <swift-evolution@swift.org> wrote:
>
> Currently, we parse a type after 'as[?!]' and 'is'. This is mostly what you'd
> expect, but does lead to problems when an 'as' expression appears as part of
> a comparison:
>
> 20 as Int64 < y as Int64 // error, '>' expected to close generic parameter
> list Int64<y>
>
> Looking to the future, many people have also expressed interest in the
> ability to do dynamic type checks against metatype values, not only static
> types, as in:
>
> class Base {}
> class DerivedA {}
> class DerivedB {}
>
> var x: Base.Type = DerivedA
>
> DerivedA() as? x // succeeds
> DerivedB() as? x // fails
>
> If we accept
> https://github.com/apple/swift-evolution/blob/master/proposals/0090-remove-dot-self.md,
> dropping the '.self' requirement to refer to type objects, then I think we
> should also change 'is' and 'as' to parse the expression grammar on their
> right-hand side, leaving it up to the normal expression disambiguation rule
> to handle angle brackets. This solves the '20 as Int64 < x' problem, and
> prepares us to support dynamic is/as queries in the future. (To be clear,
> designing dynamic queries should be its own discussion.) What do you all
> think?
>
> -Joe
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