There is an option for avoiding if() checks in client code at all. All you have to do is to implement operator<< for logger class.
[...]
And then in client code:
logger("app.gui") << "something GUIsh";
Though I am not sure, if a compiler will be able to optimize checks for every operator<<() to a single check for the entire output expression.
Now replace "something GUIsh" with anExpensiveFunction(). John's code will not evaluate it when the logger is disabled. OTOH your code will always evaluate it, which is IMHO not acceptable for a logging library.
Yes, that's what I want to avoid. Thanks Daniel. Best, John -- John Torjo, Contributing editor, C/C++ Users Journal -- "Win32 GUI Generics" -- generics & GUI do mix, after all -- http://www.torjo.com/win32gui/ -- v1.5 - tooltips at your fingertips (work for menus too!) + bitmap buttons (work for MessageBox too!) + tab dialogs, hyper links, lite html