[swift-evolution] [Proposal] Improving operator requirements in protocols

[Tony Allevato]

On Mon, May 2, 2016 at 1:20 PM Dave Abrahams via swift-evolution <
swift-evolution at swift.org> wrote:

>
> Tony, thanks for writing this up!
>
> on Mon May 02 2016, Tony Allevato <swift-evolution at swift.org> wrote:
>
> > Other kinds of operators (prefix, postfix, assignment)
> >
> > Static operator methods have the same signatures as their global
> counterparts.
> > So, for example, prefix and postfix operators as well as assignment
> operators
> > would be defined the way one would expect:
> >
> > protocol SomeProtocol {
> >   static func +=(lhs: inout Self, rhs: Self)
> >   static prefix func ~(value: Self) -> Self
> >
> >   // This one is deprecated, of course, but used here just to serve as an
> >   // example.
> >   static postfix func ++(value: inout Self) -> Self
> > }
> >
> > // Trampolines
> > func += <T: SomeProtocol>(lhs: inout T, rhs T) {
> >   T.+=(&lhs, rhs)
> > }
> > prefix func ~ <T: SomeProtocol>(value: T) -> T {
> >   return T.~(value)
> > }
> > postfix func ++ <T: SomeProtocol>(value: inout T) -> T {
> >   return T.++(&value)
> > }
>
> How does one distinguish between calls to a static prefix operator and a
> static postfix operator with the same name?
>

Ah, that's a tricky one that I don't have an immediate answer to, so I'm
definitely open to creative thoughts here.

The first stab I would take at is, what if we included the token "prefix"
or "suffix" before the operator name in the expression, like this?

    return T.prefix ++(&value)
    return T.postfix ++(&value)

But that could start to look like an invocation of "++" on a static
property "T.prefix". I haven't dug into the parser to determine if that
would even be feasible or not.
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