That's a solved problem. Your logger should be capable of formatting on it's own, and take the arguments to the format string as variadic arguments. This is how Java's ubiquitous SLF4J interface is defined. If the log level isn't low enough, then the arguments are tossed but never composited.
And it's even better with languages with macros, like Rust, Scala, even C++. There won't be any function call to begin with if the corresponding logging level is not enabled, only a branch.
