Tuple == Confusion

Question

Suppose I define two tuples:

Tuple<float, float, float, float> tuple1 = new Tuple<float, float, float, float>(1.0f, 2.0f, 3.0f, 4.0f);
Tuple<float, float, float, float> tuple2 = new Tuple<float, float, float, float>(1.0f, 2.0f, 3.0f, 4.0f);

If I try to compare the tuples, I get different results

bool result1 = (tuple1 == tuple2);    // FALSE
bool result2 = tuple1.Equals(tuple2); // TRUE

I would expect for both calls to return true. What exactly is == comparing?

Answer 1

For Tuple, the == is comparing the object references because it does not overload the == operator. Since the objects are equivalent, but not the same specific instance, Equals() returns true and == returns false.

Many types do not overload ==, some prefer to keep a distinction between Equals() for equivalence and == for reference equality.

In addition, relying on == for equivalence can lead to some weirdness:

public bool AreSame<T>(T first, T second) where T : class
{
    return first == second;
}

The code above will always check for reference equality because an unconstrained generic is considered an object at compile time, thus if the method isn't virtual, you will get object's version (even if the type, such as string overloads ==).

Thus this usage of the above code:

var x = "Hello";
var y = "H";

// doing concat to avoid string interring
AreSame(x, y+"ello");

Yes, the strings are equivalent, yes T is string, but the == is bound to object's == since the generic is unconstrained, thus this will return false even though the same code with explicit string parameters would return true.