Struct与赋值

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using System;
using System.Collections.Generic;
 
struct SomeStruct
{
    public int SomeValue;
}
 
class SomeContainerClass
{
    public SomeStruct Struct;
}
 
struct SomeContainerStruct
{
    public SomeStruct Struct;
}
 
class Program
{
    static void Main()
    {
        TestStruct();
        TestClass();
        TestArray();
        TestList();
 
        Console.ReadKey();
    }
 
    static SomeStruct GetDefaultValue()
    {
        return new SomeStruct { SomeValue = 100 };
    }
 
 
    private static void TestStruct()
    {
        ShowTestName("TestStruct:");
        var c = new SomeContainerStruct { Struct = GetDefaultValue() };
        ShowResult("original:", c.Struct.SomeValue);
 
        var s = c.Struct;
        s.SomeValue = 200;
        ShowResult("indirectly:", c.Struct.SomeValue);
 
        c.Struct.SomeValue = 300;
        ShowResult("directly:", c.Struct.SomeValue);
    }
 
    private static void TestClass()
    {
        ShowTestName("TestClass:");
        var c = new SomeContainerClass { Struct = GetDefaultValue() };
        ShowResult("original:", c.Struct.SomeValue);
 
        var s = c.Struct;
        s.SomeValue = 200;
        ShowResult("indirectly:", c.Struct.SomeValue);
 
        c.Struct.SomeValue = 300;
        ShowResult("directly:", c.Struct.SomeValue);
    }
 
    private static void TestArray()
    {
        ShowTestName("TestArray:");
        var c = new[] { GetDefaultValue() };
        ShowResult("original:", c[0].SomeValue);
 
        var s = c[0];
        s.SomeValue = 200;
        ShowResult("indirectly:", c[0].SomeValue);
 
        c[0].SomeValue = 300;
        ShowResult("directly:", c[0].SomeValue);
    }
 
    private static void TestList()
    {
        ShowTestName("TestList:");
        var c = new List<SomeStruct> { GetDefaultValue() };
        ShowResult("original:", c[0].SomeValue);
 
        var s = c[0];
        s.SomeValue = 200;
        ShowResult("indirectly:", c[0].SomeValue);
 
        //the follow line won't compile
        //Cannot modify the return value of 'System.Collections.Generic.List<StructTest.SomeStruct>.this[int]' because it is not a variable
        //c[0].SomeValue = 300;
        //ShowTestName("directly:", c[0].SomeValue);
    }
 
 
    static void ShowResult(string condition, int value)
    {
        Console.Write(condition);
        Console.Write("\t");
        Console.WriteLine(value);
    }
 
    static void ShowTestName(string message)
    {
        Console.WriteLine();
        Console.WriteLine(message);
    }
 
}