匿名命名空间

Question

A recent thread on SO triggerred this.

An anonymous namespace is considered to be equivalent to

  namespace unique { /* empty body */ } 
  using namespace unique; 
  namespace unique { namespace-body }

I fail to recollect the exact reason as to why it is not equivalent to

  namespace unique { namespace-body } 
  using namespace unique;

Also tried searching (including google) but in vain. Please share any information you have in this regards.

Answer 1

The specification that exists now was introduced in 1995 in N0783 to correct for a corner case. To quote that paper (page 9):

The WP defines the semantics of an unnamed namespace as being equivalent to:

 namespace UNIQUE { // namespace body } using namespace UNIQUE; 

This is incorrect because it makes the code in an unnamed namespace dependent on whether the code is in an original namespace or a namespace extension.

 namespace {} // If you remove this line, the // use of ::f below is invalid namespace { void f() { using ::f; } } 

The WP should be changed to define an unnamed namespace as being equivalent to:

 namespace UNIQUE {} using namespace UNIQUE; namespace UNIQUE { // namespace body }