foo-impl.h

// This is where you would put implementation details of your library
// It is recommended to only put public header files in the include/ folder, that is files that are required
// to use your library. I suggest using the pitchfork layout which can be found here:
// https://api.csswg.org/bikeshed/?force=1&url=https://raw.githubusercontent.com/vector-of-bool/pitchfork/develop/data/spec.bs