Swift只读外部，读写内部属性 [英] Swift readonly external, readwrite internal property

问题描述

在Swift中，定义公共模式的常规方式是什么，在该模式中，属性是外部只读的，但可以由拥有该属性的类(和子类)在内部进行修改.

In Swift, what is the conventional way to define the common pattern where a property is to be externally readonly, but modifiable internally by the class (and subclasses) that own it.

在Objective-C中，有以下选项:

In Objective-C, there are the following options:

• 在接口中将该属性声明为只读，并使用类扩展名在内部访问该属性.这是基于消息的访问，因此可以很好地与KVO，原子性等配合使用.
• 在接口中将该属性声明为只读，但在内部访问后备ivar.由于对ivar的默认访问受到保护，因此在类层次结构中效果很好，在该类层次结构中，子类也可以修改值，但该字段为只读.

在Java中，约定为:

In Java the convention is:

• 声明一个受保护的字段，并实现一个公共的只读getter(方法).

Swift的成语是什么?

What is the idiom for Swift?

推荐答案

给定一个类属性，您可以通过在属性声明前面加上access修饰符并在括号之间使用get或set来指定不同的访问级别.例如，具有公共获取器和私有设置器的类属性将声明为:

Given a class property, you can specify a different access level by prefixing the property declaration with the access modifier followed by get or set between parenthesis. For example, a class property with a public getter and a private setter will be declared as:

private(set) public var readonlyProperty: Int

建议阅读: Martin关于可访问性级别的考虑仍然有效-即没有protected修饰符，internal仅限制对模块的访问，private仅对当前文件的访问，以及public没有限制.

Martin's considerations about accessibility level are still valid - i.e. there's no protected modifier, internal restricts access to the module only, private to the current file only, and public with no restrictions.

2个新的访问修饰符fileprivate和open，而对private和public进行了一些修改:

2 new access modifiers, fileprivate and open have been added to the language, while private and public have been slightly modified:

• open仅适用于类和类成员:它用于允许对类进行子类化或在定义它们的模块之外重写成员. public而是使类或成员可公开访问，但不能继承或覆盖

• open applies to class and class members only: it's used to allow a class to be subclassed or a member to be overridden outside of the module where they are defined. public instead makes the class or the member publicly accessible, but not inheritable or overridable

private现在使成员仅从封闭的声明中可见并可以访问，而fileprivate到包含该成员的整个文件

private now makes a member visible and accessible from the enclosing declaration only, whereas fileprivate to the entire file where it is contained

更多详细信息这里.

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