Can function objects be passed as arguments for a closure-typed parameter?

Using Swift
1

We've recently added the capability for objects to be called as functions by adding a method to a nominal type with a base name of "callAsFunction" and any desired parameter tuple. Can such objects be used for code that takes in a closure? I haven't tried it; it's just a thought experiment right now. One part of me thinks they should not match because a closure is a function type and a nominal type with callAsFunction still isn't a function type. Another part of me thinks they should match because the feature would be 99% useless otherwise.

Which way is it? And if it's allowed, how does that get past the type checker?

2

No, such an implicit conversion is not currently supported.

3

No, you cannot do that yet.

struct S {
  func callAsFunction() {}
}

func method(_: () -> Void) {}

let s = S()
method(s) // error
4

Well, you could use x.callAsFunction.

6 Likes
5

Would this extend the lifetime of x?

6

It would strongly capture x (as it should), so yes, x would at least outlive the function.

1 Like