C++ Coding Standards: 101 Rules, Guidelines, and Best Practices

58. Keep types and functions in separate namespaces unless they’re specifically intended to work together

Summary

Help prevent name lookup accidents: Isolate types from unintentional argument-dependent lookup (ADL, also known as Koenig lookup), and encourage intentional ADL, by putting them in their own namespaces (along with their directly related nonmember functions; see Item 57). Avoid putting a type into the same namespace as a templated function or operator.

Discussion

By following this advice, you will avoid having to track down hard-to-diagnose errors in your code and avoid having to know about excessively subtle language details that you, well, should never have to know about.

Consider this actual example that was posted publicly to ...