Swift 有访问修饰符吗? [英] Does Swift have access modifiers?

问题描述

在 Objective-C 中，实例数据可以是 public、protected 或 private.例如:

In Objective-C instance data can be public, protected or private. For example:

@interface Foo : NSObject
{
  @public
    int x;
  @protected:
    int y;
  @private:
    int z;
  }
-(int) apple;
-(int) pear;
-(int) banana;
@end

我在 Swift 参考中没有发现任何提及访问修饰符的内容.是否可以在 Swift 中限制数据的可见性?

I haven't found any mention of access modifiers in the Swift reference. Is it possible to limit the visibility of data in Swift?

推荐答案

自 Swift 3.0.1 起，有 4 个访问级别，如下所述，从最高(限制最少)到最低(最限制性).

As of Swift 3.0.1, there are 4 levels of access, described below from the highest (least restrictive) to the lowest (most restrictive).

允许在定义模块(目标)之外使用实体.在指定框架的公共接口时，您通常使用 open 或 public 访问.

Enable an entity to be used outside the defining module (target). You typically use open or public access when specifying the public interface to a framework.

但是，open访问只适用于类和类成员，它与public访问的区别如下:

However, open access applies only to classes and class members, and it differs from public access as follows:

• public 类和类成员只能在定义模块(目标)内被子类化和覆盖.
• open 类和类成员可以在定义模块(目标)内部和外部进行子类化和覆盖.

• public classes and class members can only be subclassed and overridden within the defining module (target).
• open classes and class members can be subclassed and overridden both within and outside the defining module (target).

// First.framework – A.swift

open class A {}

// First.framework – B.swift

public class B: A {} // ok

// Second.framework – C.swift

import First

internal class C: A {} // ok

// Second.framework – D.swift

import First

internal class D: B {} // error: B cannot be subclassed

2.内部

使实体能够在定义模块(目标)中使用.在定义应用或框架的内部结构时，您通常使用 internal 访问权限.

// First.framework – A.swift

internal struct A {}

// First.framework – B.swift

A() // ok

// Second.framework – C.swift

import First

A() // error: A is unavailable

3.fileprivate

将实体的使用限制在其定义的源文件中.当在整个文件中使用这些细节时，您通常使用 fileprivate 访问来隐藏特定功能的实现细节.

3. fileprivate

Restricts the use of an entity to its defining source file. You typically use fileprivate access to hide the implementation details of a specific piece of functionality when those details are used within an entire file.

// First.framework – A.swift

internal struct A {

    fileprivate static let x: Int

}

A.x // ok

// First.framework – B.swift

A.x // error: x is not available

4.私有

将实体的使用限制在其封闭声明中.当特定功能的实现细节仅在单个声明中使用时，您通常使用私有访问来隐藏这些细节.

// First.framework – A.swift

internal struct A {

    private static let x: Int

    internal static func doSomethingWithX() {
        x // ok
    }

}

A.x // error: x is unavailable

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