如何测试命名元组的Swift数组的相等性

@L_502_0@元组不是Equatable,而作为复合类型,它们不能通过协议扩展来制作Equatable.解决方法( as documented in another answer)是为每个元组元素的==运算符创建重载.

有趣的是,可以为常规元组声明==运算符,并使用它来将元组与命名字段进行比较：

func ==<T1: Equatable,T2: Equatable>(lhs: (T1,T2),rhs: (T1,T2)) -> Bool {
    return lhs.0 == rhs.0 && lhs.1 == rhs.1
}

var one = ("One",1)
let two = ("Two",2)
print(one == two) // "false"

typealias NamedTuple2 = (name: String,value: Int)
var namedone: NamedTuple2 = (name: "One",value: 1)
let namedtwo: NamedTuple2 = (name: "Two",value: 2)
print(namedone == namedtwo) // "false"
print(namedone == one) // "true"

元组数组也需要自定义重载作为整体进行比较：

func ==<T0: Equatable,T1: Equatable>(lhs: [(T0,T1)],rhs: [(T0,T1)]) -> Bool {
    if lhs.count != rhs.count {
        return false
    }
    for (index,value) in lhs.enumerate() {
        if !(value == rhs[index]) {
            return false
        }
    }
    return true
}

let array12: [(String,Int)] = [one,two]
let array3: [Tuple2] = [("Three",3)]
print(array12 == array3) // "false"

但是,此运算符不接受命名元组的数组：

let namedarray12: [NamedTuple2] = [namedone,namedtwo]
let namedarray3: [NamedTuple2] = [array3[0]]
print(namedarray12 == namedarray3)
// error: binary operator '==' cannot be applied to two '[NamedTuple2]' operands

有没有办法测试命名元组数组的相等性,而不为特定的命名元组声明==的重载？

解决方法

SequenceType.elementsEqual(_,isEquivalent :)方法接受用于比较元素的谓词.相同的==重载适用于命名和未命名的元组.因此,不要尝试将==作为整体应用于数组,而是使用elementsEqual.

func ==<T1: Equatable,T2)) -> Bool {
    return lhs.0 == rhs.0 && lhs.1 == rhs.1
}

let namedarray: [(name: String,value: Int)] = [(name: "One",value: 1),(name: "Two",value: 2)]
// namedarray == namedarray12
namedarray.elementsEqual(namedarray12,isEquivalent: ==) // true