CODEWITHSUNDEEP
c++visual-c++clangstandards
joshbodily
joshbodily

Reputation: 1093

Xcode inferring namespace?

namespace Foo {
  class Bar { };
}

namespace Foo {
  namespace Foo {
    class FooFooClass {
      public:
        void do_stuff(Bar& key);
    };
  }
}

using namespace Foo::Foo;

void FooFooClass::do_stuff(Bar& key) {

}

The preceding snippet compiles in XCode, but does not compile in Visual Studio (fails on 3rd to last line with 'Bar': undeclared identifier) which one is more correct according to the C++ Standard. I'm assuming that clang is inferring the correct namespace for Bar in a proprietary non-standard-following way?

Upvotes: 2

Views: 323

Answers (1)

Brian Bi
Brian Bi

Reputation: 119457

Clang is correct, due to an obscure but useful rule in the standard ([basic.lookup.qual]/3):

In a declaration in which the declarator-id is a qualified-id, names used before the qualified-id being declared are looked up in the defining namespace scope; names following the qualified-id are looked up in the scope of the member’s class or namespace.

That is, as soon as the compiler sees that the entity being defined, FooFooClass::do_stuff, is a member of a class, it looks up all following names in that declaration in the scope of FooFooClass. That means lookup of Bar starts by looking for a member of Foo::Foo::FooFooClass, then a member of Foo::Foo, then a member of Foo, then the global scope. Since Bar is found in Foo, the name lookup succeeds.

Upvotes: 2

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