1

Hi all
I've tried to make a function with @autoclosure for optional closure like func foo(myArg: @autoclosure (() -> String)? = nil) but got an error @autoclosure attribute only applies to function types.
Is there any way to do it or I do it in a wrong way?

2

Could you do something like

func t(_ b: @autoclosure () -> String?) -> String {
  return b() ?? "hello"
}

print(t(nil))
3

Unfortunately, not. I need this optional to make the rest system work as expected.

4

Then no, you can't currently use @autoclosure like this, so you'll have to manually create the closures. Which is the same effect, but without the nice syntactic sugar.

5

Is it an acceptable solution to make two separate methods where one calls the other with nil?

foo() {
foo(myArg: nil)
}
foo(myArg: @autoclosure () -> String) = nil)
6

I'm not aware of a way to do this, but extending swift to support this would be reasonable and inline with how @escaping works.

-Chris

7 Likes
7

Wouldn't it make ambiguous constructs ?

func foo(args: @autoclosure (() -> String?)?) {}

foo(args: nil)

Should it call foo with args = nil or should it call it with arg = { return nil } ?

4 Likes
8

Very good question.

May be it makes sense to use nil as args = nil? What is the process to discuss this with community?

9

We should just allow this instead of come up with new hacks:

func foo(bar: (@autoclosure () -> String)? = nil) { ... }

var something: @autoclosure () -> String
6 Likes
10

I came into a situation today where I would have liked to have this.

2 Likes
11

This construction seems to work:

func foo(value: @autoclosure () -> Int? = { nil }()) {
    //...
}
2 Likes