C＃：为什么在只读结构突变不破？ [英] C#: Why do mutations on readonly structs not break?

问题描述

在C＃中，如果你有一个结构像这样：

In C#, if you have a struct like so:

struct Counter
{
    private int _count;

    public int Value
    {
        get { return _count; }
    }

    public int Increment()
    {
        return ++_count;
    }
}

和你有一个程序，像这样：

And you have a program like so:

static readonly Counter counter = new Counter();

static void Main()
{
    // print the new value from the increment function
    Console.WriteLine(counter.Increment());
    // print off the value stored in the item
    Console.WriteLine(counter.Value);
}

该程序的输出将是：

The output of the program will be:

1
0

这似乎是完全错误的。我要么期望的输出是两个1（因为它是，如果计数是类或者结构计数器：ICounter 和计数是 ICounter ），或者是编译错误。我认识到，在编译时检测到这是一个相当困难的事情，但这种行为似乎违反逻辑。

This seems completely wrong. I would either expect the output to be two 1s (as it is if Counter is a class or if struct Counter : ICounter and counter is an ICounter) or be a compilation error. I realize that detecting this at compilation time is a rather difficult matter, but this behavior seems to violate logic.

有没有超越实现难度此行为的原因是什么？

Is there a reason for this behavior beyond implementation difficulty?

推荐答案

结构是值类型，所以具有值类型语义学。这意味着每次访问你基本上与该结构的值的副本的工作结构的时间。

structs are value types and therefore have a value type sematics. This means each time you access the struct you basically work with a copy of the struct's value.

在您的样品你不改变原 。结构，但只有它的临时副本

In your sample you don't change the original struct but only a temporary copy of it.

在这里看到进一步的解释：

See here for further explanations:

为什么是可变的结构邪恶

Why are mutable structs evil

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