Swift 中受保护的访问级别

在 Swift 中，我们可以使用访问控制来限制代码的访问级别。通过使用不同的访问级别，我们可以确保代码的安全性和可维护性。Swift 中的受保护的访问级别包括私有访问级别、文件私有访问级别、内部访问级别和公开访问级别。让我们逐一了解这些访问级别，并看看如何在代码中使用它们。

swift
class MyClass {
    private var privateVar = 10
    
    private func privateMethod() {
        print("This is a private method.")
    }
    
    func publicMethod() {
        print("This is a public method.")
        privateMethod()
    }
}
let myObject = MyClass()
myObject.publicMethod() // 输出："This is a public method." \n "This is a private method."
myObject.privateVar // 编译错误：'privateVar' is inaccessible due to 'private' protection level
myObject.privateMethod() // 编译错误：'privateMethod' is inaccessible due to 'private' protection level

swift
fileprivate struct MyStruct {
    fileprivate var fileprivateVar = 20
    
    fileprivate func fileprivateMethod() {
        print("This is a fileprivate method.")
    }
    
    func publicMethod() {
        print("This is a public method.")
        fileprivateMethod()
    }
}
let myStructObject = MyStruct()
myStructObject.publicMethod() // 输出："This is a public method." \n "This is a fileprivate method."
myStructObject.fileprivateVar // 编译错误：'fileprivateVar' is inaccessible due to 'fileprivate' protection level
myStructObject.fileprivateMethod() // 编译错误：'fileprivateMethod' is inaccessible due to 'fileprivate' protection level

swift
internal class MyInternalClass {
    internal var internalVar = 30
    
    internal func internalMethod() {
        print("This is an internal method.")
    }
    
    func publicMethod() {
        print("This is a public method.")
        internalMethod()
    }
}
let myInternalObject = MyInternalClass()
myInternalObject.publicMethod() // 输出："This is a public method." \n "This is an internal method."
myInternalObject.internalVar // 输出：30
myInternalObject.internalMethod() // 输出："This is an internal method."

swift
public enum MyPublicEnum {
    public var publicVar = 40
    
    public func publicMethod() {
        print("This is a public method.")
    }
    
    func internalMethod() {
        print("This is an internal method.")
    }
}
let myPublicEnumObject = MyPublicEnum()
myPublicEnumObject.publicMethod() // 输出："This is a public method."
myPublicEnumObject.internalMethod() // 编译错误：'internalMethod' is inaccessible due to 'internal' protection level
myPublicEnumObject.publicVar // 输出：40