using System;
 
public class Test
{
	class ClassA
	{
	    public string Value1 { get; protected set; }
 
	    // コンストラクタ
	    public ClassA(string val) { Value1 = val; }
 
	    // == 演算子を定義
	    public static bool operator==(ClassA self, ClassA other)
	    {
	        return self.Value1 == other.Value1;
	    }
	    // == を定義するためには != もペアで定義が必要
	    public static bool operator!=(ClassA self, ClassA other)
	    {
	        return !(self == other);
	    }
	}
 
	// ClassA を継承したクラス
	class ClassB : ClassA
	{
	    public int Value2 { get; protected set; }
 
	    public ClassB(string val1, int val2) : base(val1) { Value2 = val2; }
 
	    // == をオーバーライド？（実は出来ていない）
	    public static bool operator==(ClassB self, ClassB other)
	    {
	        return self.Value1 == other.Value1 && self.Value2 == other.Value2;
	    }
	    // == を定義するためには != もペアで定義が必要
	    public static bool operator!=(ClassB self, ClassB other)
	    {
	        return !(self == other);
	    }
	}
 
    static void Main(string[] args)
    {
        // ClassA のインスタンスを比較
        var a1 = new ClassA("A");
        var a2 = new ClassA("A");
 
        Console.WriteLine(a1 == a2);  // True
 
        // ClassB のインスタンスを比較
        var b1 = new ClassB("1", 10);
        var b2 = new ClassB("1", 20);
 
        Console.WriteLine(b1 == b2);  // False  <= Value2 の値が異なるので False
 
        // ClassA 型の変数に代入（キャスト）
        ClassA c1 = b1;
        ClassA c2 = b2;
 
        Console.WriteLine(c1 == c2);  // True  <= ここで、ClassAの==演算子が呼ばれている
 
        Console.WriteLine($"{c1.GetType().Name}, {c2.GetType().Name}");  // ClassB, ClassB  <= 実体はどちらもClassB
    }
}
 

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