[swift-evolution] Splat

[Thorsten Seitz]

I really like the apply-variant, especially as it moves functions one step into being first class, i.e. allowing them to have methods. Furthermore I like that it does not need new syntax.
The Applicable protocol is a good idea.

-Thorsten 


Am 11.02.2016 um 08:54 schrieb Brent Royal-Gordon via swift-evolution <swift-evolution at swift.org>:

>> Still find it quite confusing, because I expected x.methodName to be a bound method and here it's a special syntactic form.  What happens if a protocol defines "func apply(to:)"?  Is that legal?  Would function types automatically conform to the protocol?
> 
> For `apply(to:)`, it really would just be a method available on function types. You could put an `apply(to:)` method on any other type, and it wouldn't have any effect on things. You could declare a protocol with `apply(to:)`, but it wouldn't do anything to any function types. Conceptually, there would only be a few special things about them:
> 
> 1. The compiler generates the `apply(to:)` methods automatically. We could, perhaps, have it generate a conformance to an `Applicable` protocol like this one, but that's probably overkill:
> 
>    protocol Applicable {
>        typealias ReturnValue
>        typealias ArgumentTuple
>        func apply(to: ArgumentTuple) -> ReturnValue
>    }
> 
> (Actually, as I think about this, I wonder if `Applicable` could give us the `@splatting` property for free: take a generic parameter on Applicable and someone can specify a bare function, but you can't call it directly, only through its `apply(to:)` method.)
> 
> 2. If `fn` is overloaded, `fn.apply(x)` will end up selecting an `fn` overload based on the type of `x`. Concrete example: `(+).apply(tupleOfInts)` would give you the `Int, Int` implementation of the `+` operator.
> 
> 3. There's no way to add your own methods to a function type. (At least, I'm not proposing there would be. There's no particular reason we couldn't have other methods on functions, particularly if there's an `Applicable` protocol to extend.)
> 
> But `apply` is not a keyword, `apply(to:)` does not receive any special parsing, and you can still splatter `apply`s all around your code with no consequences whatsoever. Honestly, that's the main virtue of the `apply(to:)` suggestion: that there's really very little to it.
> 
> -- 
> Brent Royal-Gordon
> Architechies
> 
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