Swift 中的“open"关键字是什么? [英] What is the 'open' keyword in Swift?

问题描述

ObjectiveC.来自标准库的 .swift 文件在第 228 行附近包含以下几行代码:

The ObjectiveC.swift file from the standard library contains the following few lines of code around line 228:

extension NSObject : Equatable, Hashable {
  /// ...
  open var hashValue: Int {
    return hash
  }
}

open var 在这种情况下是什么意思，或者通常的 open 关键字是什么?

What does open var mean in this context, or what is the open keyword in general?

推荐答案

open 是 Swift 3 中的新访问级别，随实现一起引入的

open is a new access level in Swift 3, introduced with the implementation of

• SE-0117 允许区分公共访问和公共可覆盖性

从 2016 年 8 月 7 日起随 Swift 3 快照一起提供，并使用 Xcode 8 beta 6.

It is available with the Swift 3 snapshot from August 7, 2016, and with Xcode 8 beta 6.

简而言之:

• open 类在定义模块.open 类成员可访问并且可覆盖在定义模块之外.
• public 类可访问，但不可子类在定义模块.public 类成员可访问，但是在定义模块之外不可覆盖.

• An open class is accessible and subclassable outside of the defining module. An open class member is accessible and overridable outside of the defining module.
• A public class is accessible but not subclassable outside of the defining module. A public class member is accessible but not overridable outside of the defining module.

所以 open 就是之前的 publicSwift 发布，public 的访问受到了限制.或者，正如克里斯·拉特纳所说SE-0177:允许区分公共访问和公共覆盖:

So open is what public used to be in previous Swift releases and the access of public has been restricted. Or, as Chris Lattner puts it in SE-0177: Allow distinguishing between public access and public overridability:

开放"现在只是比公开更公开"，提供了一个非常简单和干净的模型.

"open" is now simply "more public than public", providing a very simple and clean model.

在您的示例中，open var hashValue 是一个可访问且可以在 NSObject 子类中覆盖的属性.

In your example, open var hashValue is a property which is accessible and can be overridden in NSObject subclasses.

有关更多示例和详细信息，请查看 SE-0117.

For more examples and details, have a look at SE-0117.

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