[Swift]値付きのenum値同士がイコールかどうかを判定する方法

• Xcode6.3 + Swift 1.2 + Playground

値付きでなければ何も気にせずとも判定可能

import UIKit

enum Fruits {
    case Apple
    case Orange
}

let a = Fruits.Apple
let b = Fruits.Orange

println(a == b) // "false"
println(a == .Apple) // "true"

値付きだとコンパイルエラーとなる

enum ServerResponse {
    case Result(String, String)
    case Error(String)
}

let a = ServerResponse.Result("6:00 am", "8:09 pm")
let b = ServerResponse.Error("Out of cheese.")

println(a == b)

エラー

error: binary operator '==' cannot be applied to two ServerResponse operands
println(a == b)
        ^

解決方法（一例）

==演算子を書けばOK。

import UIKit

enum ServerResponse: Equatable {
    case Result(String, String)
    case Error(String)
}

func ==(a: ServerResponse, b: ServerResponse) -> Bool {
    switch (a, b) {
    case let (.Result(a0, a1), .Result(b0, b1)):
        return a0 == b0 && a1 == b1
    case let (.Error(a0), .Error(b0)):
        return a0 == b0
    default:
        return false
    }
}

let a = ServerResponse.Result("6:00 am", "8:09 pm")
let b = ServerResponse.Error("Out of cheese.")

println(a == b) // "false"
println(a == .Result("6:00 am", "hoge")) // "false"
println(a == .Result("6:00 am", "8:09 pm")) // "true"

ただ、毎回書くのは面倒くさいですね。

参考

• How to test equality of Swift enums with associated values