在 Swift 3 中，比较两个闭包的方法是什么?

In Swift 3, what is a way to compare two closures?(在 Swift 3 中，比较两个闭包的方法是什么?)

问题描述

假设你在 Swift 3 中有两个 (Int)->() 类型的闭包，并测试它们是否相同:

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")
}

编译失败，提示:

二元运算符 '==' 不能应用于两个 '(Int)->()' 操作数

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

好的，那么我们如何比较两个相同类型的闭包，看看它们是否相同?

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

推荐答案

如果你想跟踪自己的闭包，将它们用作字典键等，你可以使用这样的东西:

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

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