内存管理/Memory Management

Code (even non-production, tutorial demo code) should not create reference cycles. Analyze your object graph and prevent strong cycles with weak and unowned references. Alternatively, use value types (struct, enum) to prevent cycles altogether.

代码（即使是非生产环境、教程演示的代码）都不应该出现循环引用。分析你的对象关系图并用 weak 和 unowned 来防止循环引用。或者使用值类型（struct、enum）来杜绝循环引用。

延长对象的生命周期/Extending object lifetime

Extend object lifetime using the [weak self] and guard let self = self else { return } idiom. [weak self] is preferred to [unowned self] where it is not immediately obvious that self outlives the closure. Explicitly extending lifetime is preferred to optional chaining.

使用惯用语法 [weak self] 和 guard let self = self else { return } 来延长对象的生命周期。 在 self 超出闭包生命周期不明确的情况下，优先使用 [weak self] 而不是 [unowned self]。利用固定代码明确延长对象的生命周期优于可选链的书写方式。

推荐（Preferred）:

resource.request().onComplete { [weak self] response in
  guard let self = self else {
    return
  }
  let model = self.updateModel(response)
  self.updateUI(model)
}

不推荐（Not Preferred）:

// might crash if self is released before response returns
resource.request().onComplete { [unowned self] response in
  let model = self.updateModel(response)
  self.updateUI(model)
}

不推荐（Not Preferred）:

// deallocate could happen between updating the model and updating UI
resource.request().onComplete { [weak self] response in
  let model = self?.updateModel(response)
  self?.updateUI(model)
}