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

This is what comes to my mind first:

• What if testing inequality is much faster than testing equality?
• What if in some cases you want to return false both for == and != (i.e. if they can't be compared for some reason)