Is return an operator or a function?

Question

This is too basic I think, but how do both of these work?

return true;   // 1 

and

return (true); // 2 

Similar: sizeof, exit

My guess:

If return was a function, 1 would be erroneous.

So, return should be a unary operator that can also take in brackets... pretty much like unary minus: -5 and -(5), both are okay.

Is that what it is - a unary operator?

Answer 1

return is a keyword that manipulates control flow. In that it's similar to if, for etc. It can be used with or without an expression (return; returns from a void function). Of course, as with all expressions, extra parentheses are allowed. (So return (42); is similar to int i = (4*10+2);, in both cases the parentheses are redundant, but allowed.)

sizeof is a keyword that is an operator, similar to new, delete, +, ->, ::, etc.

std::exit() is an identifier that denotes a function of the C standard library (which never returns to the caller).

Answer 2

return is just a language/control flow construct. It's certainly not a function, since it's syntactically irreducible, and it's not really an operator either, since it has no return value.