[swift-evolution] [Idea] Allow more operators as custom operators

[Jean-Daniel Dupas]

> Le 10 avr. 2016 à 15:01, Антон Жилин via swift-evolution <swift-evolution at swift.org> a écrit :
> 
> & (as a prefix operator), ->, ?, and ! (as a postfix operator)
> 
> This is the list of built-ins that look like operators, but are banned from use as Swift custom operators.
> 
> We can review that list.
> 
> `&` reserved as a prefix operators for a reason. It marks a variable use as `inout`, which currently cannot be done by any Swift operator function.
> 
> Other three don't have such justification.
> 
> `->`, `?` and `!` are used in types, but they are mostly unambiguous in expressions.
> 
> The only use of `!` in expressions can be rewitten as a built-in operator function:
> postfix func ! <T> (left: T!) -> T
> 
> `?` is used in optional method calls:
> a.method?(b)
> A parallel proposal is going to remove such syntax from Swift, so this will not be a problem.
> 
> `?` is also used in patterns:
> if case x? = optional { ... }
> 

While the use is unambiguous for the compiler, I’m not sure it’s going to be unambiguous for code readers. Having the same operator meaning different things depending the context is a bad idea IMHO.

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