前言

之前在 C# – 10.0 已经有介绍过 Record 了. 但之前还没怎么用到, 最近有用到了, 所以特别写多一篇. 

Class vs Struct

参考: C#详解struct和class的区别

它们最大的区别在于 Class 是引用类型, Struct 是值类型. 引用类型 (heap) vs 值类型 (stack)

定义是差不多的, 可以有 property, method, constructor 等等

public struct DimensionStruct
{
    public int Width { get; set; }
    public int Height { get; set; }
}

public class DimensionClass
{
    public int Width { get; set; }
    public int Height { get; set; }
}

在对比值和引用的时候就看区别了

var dimensionClass = new DimensionClass { Width = 100, Height = 100 };
var dimensionClass2 = dimensionClass;
var d = Object.ReferenceEquals(dimensionClass, dimensionClass2); // true
var e = Object.Equals(dimensionClass, dimensionClass2); // true
var f = Object.Equals(dimensionClass, new DimensionClass { Width = 100, Height = 100 }); // false 虽然里面 value 一样

实例指向同一个地址, Object.Equals 对比的是它们的地址是否一致, 而不是值是否一致.

在看 Struct

var dimensionStruct = new DimensionStruct { Width = 100, Height = 100 };
var dimensionStruct2 = dimensionStruct;
var a = Object.ReferenceEquals(dimensionStruct, dimensionStruct2); // false
var b = Object.Equals(dimensionStruct, dimensionStruct2); // true
var c = Object.Equals(dimensionStruct, new DimensionStruct { Width = 100, Height = 100 }); // true 值一样就行了

地址肯定是不一样的了. Object.Equals 对比的是里面的值. 值一样就行了.

When to use Struct?

我个人是没有特别感觉什么情况非用 Struct 不可.

比较常见的是 Size (width, height), Coordinate (x, y) 这类的 object value 就会用 struct.

Record

参考:

Intro to Records in C# 9 - How To Use Records And When To Use Them

Record Structs

Record Structs

Record 是 9.0 出来的.