Phantom Type @iosdc

phantom_type.swift

/*:
 ## Reference
 * [Swift: Money with Phantom Types](https://www.natashatherobot.com/swift-money-phantom-types/)
 * [Swift で Phantom Type (幽霊型)](http://qiita.com/taketo1024/items/71e3272211f08d7e0cde)
 * [Functional Snippet #13: Phantom Types](https://www.objc.io/blog/2014/12/29/functional-snippet-13-phantom-types/)
 * [Phantom Typeでコンパイル時に状態チェックする: shibuya.swift #4](https://speakerdeck.com/kazuhiro4949/phantom-typedekonpairushi-nizhuang-tai-tietukusuru-shibuya-dot-swift-number-4)
 */

import Foundation

protocol OperationState {}
class Init: OperationState {}
class Prepared: OperationState {}

private struct OperationData {
}

class HogeOperation<State: OperationState> {
    private var data: OperationData
    private init(data: OperationData) {
        self.data = data
    }
    /// いつ呼んでも良い
    func mob() {}
}

extension HogeOperation where State: Init {
    /// 一度だけ呼ぶこと
    @warn_unused_result(message="返り値: 準備済みのインスタンス")
    func prepared() -> HogeOperation<Prepared> {
        let readyOp = HogeOperation<Prepared>(data: data) // 必要なデータを引き継ぎ
        return readyOp
    }
    
    convenience init() {
        self.init(data: OperationData())
    }
}

extension HogeOperation where State: Prepared {
    /// prepare 後に呼ぶこと
    func execute() {
        /* do somethig */
    }
}

let operation = HogeOperation<Init>()
// error: 'Init' is not a subtype of 'Prepared'
//operation.execute()

let preparedOp = operation.prepared()

preparedOp.mob()
preparedOp.execute()
preparedOp.mob()
preparedOp.execute()
preparedOp.execute()