[staticfish]

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

[joveian]

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.

[cnvogel]

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;