用引用类型成员定义结构体有意义吗? [英] Does it make sense to define a struct with a reference type member?

问题描述

定义具有引用类型成员的结构体(而不是将其定义为类)是否有意义?例如，定义这个结构:

Is there any sense in defining a struct with a reference type member (and not defining it as a class)? For example, to define this struct:

public struct SomeStruct
{
    string name;
    Int32  place;
}

我之所以这么问是因为我知道结构体是一种值类型，并且在其中定义某个引用类型没有任何意义.

I asking because I know that a struct is a value type, and to define in it some reference type does not make any sense.

我说得对吗?有人能解释一下吗?

Am I right? Can someone explain this?

推荐答案

十有八九，您应该首先创建一个类而不是一个结构.例如，与您在 C++ 中可能发现的语义相比，C# 中的语义不同.大多数使用结构的程序员应该都使用过类，坦率地说，这样的问题毫无意义.

Nine times out of ten, you should be creating a class rather than a structure in the first place. Structures and classes have very different semantics in C#, compared to what you might find in C++, for example. Most programmers who use a structure should have used a class, making questions like this one quite frankly irrelevant.

这里有一些关于何时应该选择结构而不是类的快速规则:

Here are some quick rules about when you should choose a structure over a class:

1. 从不.
   ^{_{...哦，你还在读书吗?你很执着.好的，好的.}}
2. 当您明确需要值类型语义而不是引用类型语义时.
3. 当您有一个非常小的类型时(经验法则是内存占用少于 16 字节).
4. 当由您的结构表示的对象将是短暂的并且不可变(不会改变)时.
5. 有时，为了与使用结构的本机代码进行互操作.

但如果您做出了知情决定并且真正相信您do，其实需要一个结构而不是一个类，你需要重温第二点，理解什么是值类型语义.Jon Skeet 的文章在这里 应该对澄清区别大有帮助.

But if you've made an informed decision and are truly confident that you do, in fact, need a structure rather than a class, you need to revisit point number 2 and understand what value type semantics are. Jon Skeet's article here should go a long way towards clarifying the distinction.

一旦你这样做了，你应该明白为什么在值类型 (struct) 中定义引用类型不是问题.引用类型就像指针.结构内部的字段不存储实际类型；相反，它存储指向该类型的指针(或引用).使用包含引用类型的字段声明结构体并没有任何矛盾或错误.它既不会减慢对象速度"，也不会调用 GC"，这是您在评论中表达的两个问题.

Once you've done that, you should understand why defining a reference type inside of a value type (struct) is not a problem. Reference types are like pointers. The field inside of the structure doesn't store the actual type; rather, it stores a pointer (or a reference) to that type. There's nothing contradictory or wrong about declaring a struct with a field containing a reference type. It will neither "slow the object" nor will it "call GC", the two concerns you express in a comment.

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