[namespace.unnamed]

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

inline

{o p t namespace unique {/* empty body */} using namespace unique; namespace unique {namespace-body}}_{o p t 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 program.

The optional attribute-specifier-seq in the unnamed-namespace-definition appertains to unique.

[Example 1: 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]