extension of nested types

Swift ⟩ Types ⟩ Nested Types ⟩ extension of nested types

👁️ 預覽

問：「如何宣告 generic type 的 nested type 的 extension 呢？」

// ⭐️ generic type: A<T>
struct A<T> {
    let item: T
}

// ⭐️ nested type: A.B
extension A {
    struct B {
        let foo: Bool
    }
}

// ⭐️ extension of nested type
//    注意：這裡不能寫成 extension `A<T>.B`
extension A.B {
    var notFoo: Bool { return !foo }
}

// test
let a = A(item: "Hi")
let b = A<String>.B(foo: true)

print(b.notFoo)  // false

💈範例

• Emoji Memory Game 📚 - MemoryGame.Card

👥 相關

• show how to extend nested types.