> * Remove all unnecessary headers. Template expansion is slow, and preprocessing is even slower. Some of the standard includes (like `<regex>` and `<iostream>`

> * Remove all unnecessary headers. Template expansion is slow, and preprocessing is even slower. Some of the standard includes (like `<regex>` and `<iostream>`) are notorious for slowing individual translation units to a crawl. `#pragma once` for your own headers also helps with cpp-time performance. > * Forward-declare as much as you can. Forward type declarations mean that the compiler doesn't need to process all of `Foo` when it sees `Foo&` or `Foo`. I've found the include-what-you-use (IWYU) tool [1][2] can help immensely with automating this process, especially on large code-bases. It uses LLVM/Clang to analyze a .cpp file / translation unit and produces the minimal subset of exactly which includes are necessary and what types can be forward declared. [1] https://include-what-you-use.org/ https://include-what-you-use.org/ [2] https://github.com/include-what-you-use/include-what-you-use https://github.com/include-what-you-use/include-what-you-use