compare with Optional

Optional 可以直接與 non-Optional 比較，但只能用 "=="，不能用其他的 ">", "<", ">=", "<=" 等運算 (Swift 3 移除此功能 👉 SE-0121)

code

let a = [1, 2, 3, 4, 5]
let b = [1, 3, 5, 7, 9]
let c = [Int]()

// ⭐️ comparing two optionals
a.first == b.first        // true
a.last == b.last          // false
a.first == c.first        // false

// ⭐️ comparing optional with non-optional
let n = Int("23")         // Optional(23)

// ⭐️ literal `23` is inferred as `Int` then wrapped as `Optional`
//    before the comparison is performed
n == 23                    // true

📘 手冊

• Optional ⟩ operator ==

📗 參考

• 彼得潘 ⟩ optional 和非 optional 可以直接比較是否相等

• Swift Evolution ⟩ SE-0121 Remove Optional Comparison Operators

• Use Your Loaf ⟩ Swift 3 and Comparing Optionals