Just recently, I started using g_return_val_if_fail as a brief assertion
checker. It'll also exit the function with a specified return value.
But actually this introduces some weird behavior. It's configurable by
environment variables and it'll print out a log message, if the
expression didn't validate properly. But some of these assertions are
actually ment to be silent.
Using a simple macro makes it simple to structure the assertions and its
return values in a block at the start of a function or anywhere else.
