一类中的一个结构域的防护等级 [英] Protection level of a struct field within a class

问题描述

我是相当新的C＃编程所以这可​​能是一个初学者的问题。

I am fairly new to C# programming so this is likely a beginner's question.

我得到的'A.Test.That.Fails'是人迹罕至，由于其保护级别的上下面的代码错误，我不明白其中的道理。

I get a "'A.Test.That.Fails' is inaccessible due to its protection level" error on the following code snippet and I fail to understand the reason.

namespace A
{
    class Test
    {
        public void Demo()
        {
            That[] it = new That[42];
            it[0].fails = 21;
        }

        public struct That
        {
            int fails;
        }
    }
}

从C ++编程，并具有即将读取保护规则几乎是完全一样的，因为有一个单独的类我希望它的工作，即使这结构和演示<两种/ code>方法是私人。

由于侧面说明，一些页面的链接总结向C ++程序员范围和保护规则将不胜感激。

As the side note, a link to some page summing up scope and protection rules toward the C++ programmer would be greatly appreciated.

推荐答案

已经给其他的答案有你的答案，所以我赢了'T在这里打一个死马。需要声明，以便能够从外部代码访问该字段公共。

The other answers given already have your answer, so I won't beat a dead horse here. You need to declare the field public in order to be able to access it from external code.

在C ++中，结构和类是等效的，唯一的区别是它们各自的成员的缺省访问级别

In C++, structs and classes are equivalent, with the only difference being the default access level of their respective members.

然而，这不是在C＃的情况。通常情况下，你应该只使用一个结构为是不可变的（不会改变）小，短期对象。的结构具有的值类型的语义，其中作为一类具有的引用类型的语义。你理解值类型和引用类型之间的区别，如果你正在学习C＃编程是非常重要的。乔恩斯基特出版试图提供解释的文章。但是，你肯定会想拿起一个很好的入门书，C＃，在更详细的对待这些问题。

However, that's not the case in C#. Generally, you should only use a struct for small, short-lived objects that are immutable (won't change). A structure has value type semantics, where as a class has reference type semantics. It's very important that you understand the difference between value types and reference types if you're learning to program in C#. Jon Skeet has published an article that attempts to provide that explanation. But you'll definitely want to pick up a good introductory book to C# that treats these issues in more detail.

通常情况下，你要使用类在C＃，而不是一个结构。而当你使用这个类，注意微软的C＃设计指南倾向于推荐的对的公开公共字段。相反，他们建议您使用公共财产，由私人领域的支持。该准则背后的基本原理的更深入的阐述，这里给出 。例如：

More often than not, you'll want to use a class in C#, rather than a structure. And when you use that class, note that Microsoft's design guidelines for C# tend to recommend against exposing public fields. Instead, they recommend that you use a public property, backed by a private field. A more thorough exposition of the rationale behind that guideline is given here. For example:

class TimePeriod
{
    private double seconds;

    public double Seconds
    {
        get { return seconds; }
        set { seconds = value; }
    }
}

或者你可以使用简单的自动属性语法，其中有编译器自动生成私人支持字段：

Or you can use the simpler "automatic properties" syntax, which has the compiler automatically generate that private backing field:

class TimePeriod
{
    public double Seconds { get; set; }
}

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