No need to be rude! Let's get this straight: I'm not advocating for the preprocessor here. I will happily put it in the trashbin where it belongs as soon as I

No need to be rude! Let's get this straight: I'm not advocating for the preprocessor here. I will happily put it in the trashbin where it belongs as soon as I have support for modules in C++ (By the way, 90% of the code I write is written in the D programming language, which has modules, and no preprocessor). I'm advocating for interface files. Whatever mechanism you use, you still need a way to separate interface files from implementation files. Interface files can be header files, they can be java files containing a single java 'interface', they can be "D interface" files (.di). It doesn't matter which mechanism you use for this, as long as you have a way for your caller not to depend on the implementation of callee (which might, for example, directly depend on a specific audio API, for example). My point is, if you want the caller to be properly isolated from the implementation of the callee, having to maintain signatures in an interface file is unavoidable.