I don’t agree that it’s elegant. A preprocessor directive or a function attribute makes it more obvious that the code it covers may be valid only in some conditions. On the other hand, if the language optimizes some `if` statements out, you may have invalid code without noticing — and not only in the case of OS-specific code, but possibly also regular code whose `if` condition became a compile-time constant, even unintentionally/temporarily/by mistake.