Looking for a prior declaration, introduced by friend declaration

Question

There is a quote from 3.4.1/7:

When looking for a prior declaration of a class or function introduced by a friend declaration, scopes outside of the innermost enclosing namespace scope are not considered;

Can you get an example to demonstrate this rule?

Answer 1

Sure. This code works (both classes are in the same namespace):

namespace Foo {
  class Bar
  {
  friend class FooBar;
  public:
    Bar() : i(0){}
  private:
    int i;
  };

  class FooBar
  {
    FooBar( Bar & other )
    {
      other.i = 1;
    }
  };
}//namespace Foo

And this code fails (the friend class is outside of the Foo's enclosing namespace, thus the lookup fails and you see the the int Foo::i is private within this context error):

namespace Foo {
  class Bar
  {
  friend class FooBar;
  public:
    Bar() : i(0){}
  private:
    int i;
  };
}//namespace Foo

class FooBar
{
    FooBar( Foo::Bar & other )
    {
        other.i = 1;//Oops :'(
    }
};