C# generics class 操作员不工作

Question

I have a problem with generic. When I try to use less operators in generic, their call is not happening. But it works with the method Equals. That is a some test class:

public class Test
{
    public int i;

    static public Boolean operator ==(Test obj1, Test obj2)
    {
        Console.WriteLine("operator ==");
        return obj1.i == obj2.i;
    }

    static public Boolean operator !=(Test obj1, Test obj2)
    {
        Console.WriteLine("operator !=");
        return obj1.i != obj2.i;
    }

    public override bool Equals(object obj)
    {
        Console.WriteLine("operator equals");
        return this == (Test)obj;
    }

    public override int GetHashCode()
    {
        Console.WriteLine("HashCode");
        return 5;
    }
}

And class Checker:

public class Checker
{
    public Boolean TestGeneric<T>(T Left, T Right) where T : class
    {
        return Left == Right; //not work override operators
        return Left.Equals(Right); //work fine
    }
}

Small testing:

Test left = new Test() { i = 4 };
Test right = new Test() { i = 4 };
var checker = new Checker();
Console.WriteLine(checker.TestGeneric<Test>(left, right));
Console.ReadKey();

How I can use less operators in class Test from generic?

Answer 1

Overloaded operators are static methods, so they don't participate in polymorphism; they are resolved statically at compile time, based on the known type of the operands.

In a generic method, the compiler can't know that T will be Test (since it could actually be anything else), so it uses the most general definition of == , which is reference comparison.

Note that if you add a constraint on the generic method to force T to be Test or a subclass of Test , it will work as expected, but of course it won't work anymore for other types...

Answer 2

This now works in C# 11 / .NET 7 (or above):

public class Test : IEqualityOperators<Test, Test, bool>
{ /* no changes except ^^^ addition */ }

public bool TestGeneric<T>(T Left, T Right) where T : IEqualityOperators<T, T, bool>
{
    return Left == Right; // does what you expect
}