Comment by shereadsthenews

pImpl pattern is great for those who don’t care about performance but it’s inappropriate for most header libraries. You wouldn’t want a library that hides the implementation of std::vector for example. With a visible implementation the compiler compile e.g. operator[] down one x86 instruction. With a pImpl pattern it will be an indirect function call in all likelihood that will be hundreds of times slower. It can make sense for libraries where every function is really expensive anyway, but it’s ruinous for STL and the like.