• Namespaces should always be used. The main() function is the only exception. This is to avoid conflicts in the global namespace which can be particularly painful to resolve when using third-party libraries.

  • Do not use anonymous namespaces in header files, where they are at best useless, and at worst lead to undefined behavior.

  • Libraries must declare their structures and functions in a namespace (the “library namespace”) that matches the library’s name. If necessary, library internals can be placed within an internal namespace nested within the library namespace (e.g. gmath::internal). For consistency, such namespaces should be called “internal”. Apart from this, the use of nested namespaces should be avoided.

  • Avoid the use of using namespace in header files. This defeats the point of namespaces and may cause problems in the future should additional symbols get added to the included namespace.

  • using declarations are allowed for individual symbols (e.g., using std::vector;), but they should never appear in a header file. Putting a using declaration in a header file means that everybody that uses the header file will also be forced to use the declaration. Keep them in the body where they won’t bother anyone else, and even then, only after all of the #include directives.

  • Define global operators in the namespace of their parameters. You can’t specify the namespace of an operator when you’re using it, so the compiler will automatically check the namespaces of any operator arguments.

  • Namespaces are not indented.