为什么允许我使用继承了该协议的结构来设置协议的只读属性? [英] Why am I allowed to set a read only property of a protocol using a struct that inherits said protocol?

问题描述

我正在跟踪有关面向协议的编程范例的教程，在该教程中，我被一些我认为很简单的东西感到困惑，这是协议或getter和setter的只读属性.我的理解是，在协议中声明变量时，使用关键字"get"表示只读属性.我很兴奋，所以我迅速编码创建了一个游乐场，以查看我的想法是否正确，但是看来我仍然可以更改我认为是只读的属性.我将其设置为无法设置的只读属性，这是怎么做的?

I'm following a tutorial on the protocol oriented programming paradigm in which I'm confused by something I thought was rather simple which is read only properties of protocols or getters and setters. My understanding is that a read only property is signified by using the keyword 'get' when declaring a variable within a protocol. I was excited so I quickly coded created a playground to see if my thinking was accurate however it appears that I can still change the property which I thought was read only. What am I doing wrong to make it a true read only property to where I can't set it?

protocol FullName {
    var firstName: String {get set}
    var lastName: String {get set}
    var readOnlyProperty: String {get}

}

struct OuttaBeerOuttaHere: FullName {
    var firstName: String

    var lastName: String

    var readOnlyProperty: String = "Jack! Jack!...Line from Titanic"

}

var leonardoDicaprio = OuttaBeerOuttaHere.init(firstName: "Leonardo", lastName: "Dicaprio", readOnlyProperty: "WTF")

print(leonardoDicaprio.readOnlyProperty) //prints "WTF"

leonardoDicaprio.readOnlyProperty = "what now"

print(leonardoDicaprio.readOnlyProperty) //prints "what now"

推荐答案

要使它成为无法设置的只读属性，我在做错什么?

What am I doing wrong to make it a true read only property to where I can't set it?

采用协议的协议(一组规则)和类型(即您的结构)之间是有区别的.

There is a difference between a protocol (a set of rules) and the type (i.e. your struct) that adopts the protocol.

• 您的协议规则说readOnlyProperty应该可读.

您的结构遵循可读性，并且 也使其可写.那不是违法的，所以一切都很好-并且结构中的readOnlyProperty是可读写的.

Your struct obeys by making it readable, and also makes it writable. That is not illegal, so all is well — and readOnlyProperty in your struct is read-write.

将会是非法的，这将是相反的，即，协议将属性声明为可读写，而采用者则将其声明为只读.在您的示例中并没有出现这种情况，但是如果出现这种情况，编译器将阻止您.

What would have been illegal would be the inverse, i.e. for the protocol to declare a property read-write but the adopter to declare it read-only. That situation didn't arise in your example, but if it had, the compiler would have stopped you.

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