Back when I was doing C++ more often, I got a big speedup on my builds (and also smaller binaries) by using C-style forward declarations for everything that I p

Back when I was doing C++ more often, I got a big speedup on my builds (and also smaller binaries) by using C-style forward declarations for everything that I possibly could, including class methods. Method definitions / template instantiations would be placed into a corresponding .cpp file. I know that it's unpopular in a world of header-only libraries, but it really does make a dramatic difference to build-time. Especially if your code is heavy on templates.