为什么struct可以改变自己的字段? [英] Why can struct change their own fields?

问题描述

按如下方式考虑 Foo 结构:

Consider the Foo struct as follows:

struct Foo
{
  public float X;
  public float Y;

  public Foo(float x, float y)
  {
    this.X = x;
    this.Y = y;
  }

  public void Change(float x)
  {
    this.X = x;
  }
}

我理解修改构造函数中的字段，这对我来说是完全合乎逻辑的，而且我将结构体理解为值、类似数字的 immutable 类型.

I understand modifying the field in the constructor, that's perfectly logical to me and my understanding of structs as value, number-like immutable types.

然而，既然人们不能't:

Foo bar = new Foo(1, 2);
bar.X = 5;

为什么可以使用:

Foo bar = new Foo(1, 2);
bar.Change(5);

编辑:如果结构是可变的，那么为什么在列表中或从属性返回时不能修改它们?

EDIT: If structs are mutable, then why can't they be modified when in a list or returned from a property?

不能修改表达式，因为它不是变量

推荐答案

您做出了一个关键的错误假设.

You've made a key mistaken assumption.

.NET 结构是可变的.你绝对可以执行 bar.X = 5;.

.NET structs are mutable. You can absolutely perform bar.X = 5;.

您应该将结构设计为不可变的，但根据您提供的代码，它们是可变的.

You should design structs to be immutable, but by the code you have provided, they are mutable.

看看这个问题，了解可变结构在哪里会给你带来麻烦.结构的不变性

Have a look at this question for a description of where mutable structs can get your into trouble. Immutability of structs

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