In Swift 3, what is a way to compare two closures?

Question

Suppose you have two closures of type (Int)->() in Swift 3 and test to see if they are the same as each other:

typealias Baz = (Int)->()
let closure1:Baz = { print("foo \($0)") }
let closure2:Baz = { print("bar \($0)") }

if(closure1 == closure2) {
    print("equal")
}

This fails to compile, giving the message:

Binary operator '==' cannot be applied to two '(Int)->()' operands

OK, well, how then can we compare two closures of the same type, to see if they are the same?

Answer 1

In the case where you want to track your own closures, uses them as Dictionary keys, etc., you can use something like this:

struct TaggedClosure<P, R>: Equatable, Hashable {
    let id: Int
    let closure: (P) -> R

    static func == (lhs: TaggedClosure, rhs: TaggedClosure) -> Bool {
        return lhs.id == rhs.id
    }

    var hashValue: Int { return id }
}

let a = TaggedClosure(id: 1) { print("foo") }
let b = TaggedClosure(id: 1) { print("foo") }
let c = TaggedClosure(id: 2) { print("bar") }

print("a == b:", a == b) // => true
print("a == c:", a == c) // => false
print("b == c:", b == c) // => false