a problem relate to namespace and using

Re: a problem relate to namespace and using

Li Daobing wrote:[color=blue]
> Hello, I want to know whether the following program is legal. the
> g++-4.1 can not compile it
>
> $ g++ -c bug2.cpp
> bug2.cpp:8: error: expected unqualified-id before '}' token
> bug2.cpp:15: error: 'A' is already declared in this scope
> bug2.cpp:20: error: prototype for 'void n1::B::foo(cons t
> n1::n2::A&)' does not match any in class 'n1::B'
> bug2.cpp:6: error: candidate is: void n1::B::foo(cons t n1::A&)
> $
>
> // begin bug2.cpp
> // #include "b.hpp"
> namespace n1 {
> class A;[/color]

declaration of n1::A.
[color=blue]
> class B {
> void foo(const A&);
> }
> }
>
> // #include "a.hpp"
> namespace n1 {
> namespace n2 {
> class A {};
> }
> using n2::A;[/color]

using declaration of n1::A. This clashes with the n1::A declaration
above, since the two declarations refer to different classes (n1::A and
n1::n2::A).

Tom