Movatterモバイル変換

6.4 [basic.scope] paragraph 4says:

Given a set of declarations in a single declarative region, each ofwhich specifies the same unqualified name,

• they shall all refer to the same entity, or all refer to functions ...

When a declaration of a function is introduced by way of ausing-declaration (9.10 [namespace.udecl]),any default argument information associated with thedeclaration is imported as well.

    namespace A {            extern "C" void f(int = 5);    }    namespace B {            extern "C" void f(int = 7);    }    using A::f;    using B::f;    f(); // ???

Add the following at the end of 12.2.4 [over.match.best]:

If the best viable function resolves to a function for whichmultiple declarations were found, and if at least two of thesedeclarations — orthe declarations they refer to in the case ofusing-declarations — specifya default argument that made the function viable, the program is ill-formed.[Example:
    namespace A {
       extern "C" void f(int = 5);
    }
    namespace B {
       extern "C" void f(int = 5);
    }

    using A::f;
    using B::f;

    void use() {
       f(3);      // OK, default argument was not used for viability
       f();       // Error: found default argument twice
    }

  —end example]