True, but in languages with operator overloading you (may) end up with other issues. Unless you look at the source you have no idea what the '==' operator will do.

I have always wondered why all languages don't enforce this?

because, for example in C, such a incompatible change would alienate most developers used to the very ideomatic

        if((val = function(args)) != expected)
            return val;

Because it is often really convenient, particularly with a simple macro preprocessor like cpp but in other circumstances too. I like gcc's approach of forcing you (if you have the right warning enabled) to put an extra pair of unnecessary parentheses around assignments in expressions.

A better solution is gcc's which forces you (if you enable the restriction) to put an extra pair of parens around inline assignments.

The parenthesis in this attack are sufficient to prevent that warning.