See this: https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Rs-contained https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines... Technically

See this: https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Rs-contained https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines... Technically, headers are just copy-paste, obviously. However, there's value to keeping them as standalone as possible.