Why must we define both == and != in C#?

Question

The C# compiler requires that whenever a custom type defines operator ==, it must also define != (see here).

Why?

I\'m curious to k

Answer 1

Probably for if someone needs to implement three-valued logic (i.e. null). In cases like that - ANSI standard SQL, for instance - the operators can't simply be negated depending on the input.

You could have a case where:

var a = SomeObject();

And a == true returns false and a == false also returns false.