This addresses one (very uninteresting) "problem" shown by the person you are replying to. A problem which can be solved regardless of the existence of "using n

This addresses one (very uninteresting) "problem" shown by the person you are replying to. A problem which can be solved regardless of the existence of "using namespace a = b;" by simply not using the namespace. There are still all the other problems which are more concrete but which namespaces can't solve. The C standard library should have (maybe as early as C11 or C99) picked stdc_ as a "namespace", reserved it, made it a warning to put things in it, and used it for everything going forwards. What C needs is not namespaces, it's a module system, so that symbol visibility can be more tightly controlled.