unnamed namespace within named namespace

Question

Some code I've been asked to modify looks rather like this:

namespace XXX {

namespace {

// some stuff

} // end of unnamed

// Some stuff within the scope of XXX

} // end of XXX

I'm struggling to see the advantage, if any, of embedding the unnamed namespace within another namespace and I'm considering changing it to:

namespace {

// some stuff

} // end of unnamed

namespace XXX {

// Some stuff within the scope of XXX

} // end of XXX

Any views would be gratefully appreciated.

Answer 1

Okay, turns out that X::<anonymous>::foo() is visible as X::foo(). I'm surprised.

So, no, there's very little practical benefit. There may be semantic or documentation implications though.

---

Original answer

Well that rather depends on the "stuff", doesn't it?

The existing code allows code in X to have "private" other stuff that's also in X but cannot be accessed from outside of X:

#include <iostream>

namespace X {
   namespace {
      void foo() { std::cout << "lol\n"; }
   }
   
   void bar() { foo(); }
}

int main()
{
   X::bar();
   // X::foo();  // can't do this directly  [edit: turns out we can!]
}

• Output: lol\n

Your proposed approach makes that "private stuff" available to the entire translation unit:

#include <iostream>

namespace {
   void foo() { std::cout << "lol\n"; }
}

namespace X {
   void bar() { foo(); }
}

int main()
{
   X::bar();
   foo();     // works
}

• Output: lol\nlol\n