Why is this test expression an error?

Question

i want to understand why the C# language decided to make this test expression as an error.

interface IA { }
interface IB { }
class Foo : IA, IB { }
class Program
{
    static void testFunction<T>(T obj) where T : IA, IB
    {
        IA obj2 = obj;

        if (obj == obj2) //ERROR
        {

        }
    }
    static void Main(string[] args)
    {
        Foo myFoo = new Foo();
        testFunction(myFoo);
        Console.ReadLine();
    }
}

In the testFunction, i can make an object called obj2 and set it to obj implicitly without casting it. But why cant i then check the two objects to see if they are the same, without casting it? They obviously implement the same interface, so why is it an error?

Answer 1

You can check to see if they're the same object by using Object.ReferenceEquals or Object.Equals.

However, since your constraints (IA and IB interfaces) don't enforce that the type is necessarily a reference type, there's no guarantee that the equality operator can be used.