7 Declarations [dcl.dcl]

An unnamed-namespace-definition behaves as if it were replaced by

inlineopt namespace unique { /* empty body */ }
using namespace unique ;
namespace unique { namespace-body }

where inline appears if and only if it appears in the unnamed-namespace-definition and all occurrences of unique in a translation unit are replaced by the same identifier, and this identifier differs from all other identifiers in the translation unit. The optional attribute-specifier-seq in the unnamed-namespace-definition appertains to unique. [ Example:

namespace { int i; }            // unique::i
void f() { i++; }               // unique::i++

namespace A {
  namespace {
    int i;                      // A::unique::i
    int j;                      // A::unique::j
  }
  void g() { i++; }             // A::unique::i++
}

using namespace A;
void h() {
  i++;                          // error: unique::i or A::unique::i
  A::i++;                       // A::unique::i
  j++;                          // A::unique::j
}

 — end example ]