C#12：内联数组

　　之前，想把一个对象当集合使用，需要给这个类型构建索引器，为了foreach，还需要实现IEnumerable。

public struct Season : IEnumerable
{readonly string[] _arr;public Season(){_arr = new string[4];}public string this[int index]{get => _arr[index];set => _arr[index] = value;}public IEnumerator GetEnumerator(){for (var i = 0; i < _arr.Length; i++){yield return _arr[i];}}
}

　　使用时，初始化，给每个元素赋值即可，然后就可以调用foreach来循环了。

var season = new Season();
season[0] = "春";
season[1] = "夏";
season[2] = "秋";
season[3] = "冬";
foreach (var s in season)
{Console.WriteLine(s);
}

　　C#12引入了内联数组，让使用更简单，使用前，需要using ystem.Runtime.CompilerServices命名空间，然后内联数组定义如下：

[InlineArray(4)]
public struct Season
{private string _name;
}

　　使用方式无变化，并且内联数组性能更好，原因具体参照官方说明。

var season = new Season();
season[0] = "春";
season[1] = "夏";
season[2] = "秋";
season[3] = "冬";
foreach (var s in season)
{Console.WriteLine(s);
}

　　下面用BenchmarkDotNet来做个性能对比吧，完整代码如下：

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;
using System.Collections;
using System.Runtime.CompilerServices;BenchmarkRunner.Run<Demo1>();public class Demo1
{Season0 season0;Season1 season1;[GlobalSetup]public void Setup(){season0 = new Season0();season0[0] = "春";season0[1] = "夏";season0[2] = "秋";season0[3] = "冬";season1 = new Season1();season1[0] = "春";season1[1] = "夏";season1[2] = "秋";season1[3] = "冬";}[Benchmark()]public void P0(){foreach (var s in season0){var s0 = s;//Console.WriteLine(s);
        }}[Benchmark]public void P1(){foreach (var s in season1){var s0 = s;//Console.WriteLine(s);
        }}
}[InlineArray(4)]
public struct Season0
{private string _name;
}public struct Season1 : IEnumerable
{readonly string[] _arr;public Season1(){_arr = new string[4];}public string this[int index]{get => _arr[index];set => _arr[index] = value;}public IEnumerator GetEnumerator(){for (var i = 0; i < _arr.Length; i++){yield return _arr[i];}}
}

　　下图是最后的对比结果，当然这是一个很粗糙的对比，但从性能上来看，内联数组不只要强数10万倍，虽然单次调用耗时可以忽略，但有时这个功能放在大循环中，累加起来的这些时间就不能忽视了。

 

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