Swift 4.2

Question

有similar question关于如何weakify / strongify自我的问题，这已得到解答，但我想知道如何使用＆＃34; self＆＃34 ;没有if let引起的向右漂移：

Welcome to Apple Swift version 2.0 (700.0.59 700.0.72). Type :help for assistance.
  2> import Foundation
  3> class Foo {
  4.     func guardOptSelf() -> () throws -> Void {
  5.         return { [weak self] in
  6.             guard let self = self else { throw NSError(domain: "I was destroyed!", code: 1, userInfo: nil) }
  7.             self.doSomethingNonOptionalSelf()         
  8.         }
  9.     }
  10. }
repl.swift:6:19: error: pattern matching in a condition requires the 'case' keyword
            guard let self = self else { throw NSError(domain: "I was destroyed!", code: 1, userInfo: nil) }
                  ^
                  case
repl.swift:6:23: error: binary operator '~=' cannot be applied to two 'Foo?' operands
            guard let self = self else { throw NSError(domain: "I was destroyed!", code: 1, userInfo: nil) }

Answer 1

你可以影子self;你只需要反叛来表明＆＃34;你知道你在做什么＆＃34;。例如：

foo.doSomethingAsyncWithBar(bar) { [weak self] result in
    guard let `self` = self else { return }
    self.receivedResult(result)
}

或者，在您的示例中：

2> import Foundation
3> class Foo {
4.     func guardOptSelf() -> () throws -> Void {
5.         return { [weak self] in
6.             guard let `self` = self else { throw NSError(domain: "I was destroyed!", code: 1, userInfo: nil) }
7.             self.doSomethingNonOptionalSelf()         
8.         }
9.     }
10. }

Answer 2

Swift 4.2

从Swift 4.2开始，您可以使用以下语法：

{ [weak self] in
    guard let self = self else { return }

    // self is not an optional anymore, it is held strongly
}

有关更多信息，请参阅Swift evolution proposal SE-0079。

有时，除了使用guard let之外的其他方法也可能有用（例如更短或更易读）。另请参阅以下部分，只需在少数示例中将strongSelf替换为self。

Swift 4.1及更早版本

因为guard let `self` = self是compiler bug as stated by Chris Lattner，我会尽量避免它。在您的示例中，您可以使用简单的可选链接：

return { [weak self] in
    self?.doSomethingNonOptionalSelf()         
}

有时您可能需要使用self作为参数。在这种情况下，您可以使用flatMap（在可选类型上）：

{ [weak self] in
    self.flatMap { $0.delegate?.tableView($0, didSelectRowAt: indexPath) }
}

如果您需要做一些更复杂的事情，可以使用if let construct：

{ [weak self] in
    if let strongSelf = self {
        // Do something more complicated using strongSelf
    }
}

或guard let构建：

{ [weak self] in
    guard let strongSelf = self else { return }

    // Do something more complicated using strongSelf
}

或者您可以创建一个私有方法：

{ [weak self] in
    self?.doSomethingMoreComplicated()
}

...

private func doSomethingMoreComplicated() {
    // Do something more complicated
}

Answer 3

从Swift 4.2开始，您不再需要将self与反引号（编译器错误）或诸如strongSelf之类的奇怪变量名一起使用。您可以使用guard let self = self else { return }来解开weak self：

class Example {

    var closure: (() -> Void)?

    init() {
        self.closure = { [weak self] in
            guard let self = self else {
                return
            }
            // ...
        }
    }
}

您可以在Swift evolution proposal中了解更多信息。

如何强化＆＃34;在Swift 2.0中使用后卫的可选自我

3 个答案:

Swift 4.2

Swift 4.1及更早版本