Unexpected side effects of using inside a namespace

[JUAN DENT]

Hi,

I just came across the most unexpected situation and I want to share it with all of you just in case you haven't faced it yet.

I have the following code:

namespace X
{
    using namespace std;

     /////
}

void someFunc()
{
   using namespace std::chrono;

   chrono::hours hrs;
}

I get the following at compilation: Use of undeclared identifier 'chrono', did you mean X::chrono?

Wow! The using directive inside of X seemed to me be to local - never anticipated it would have consequences in following code. I now realize that all symbols U inside std become available as X::U (in other words std::U becomes synonym with X::U).

Wow! Dangerous and unexpected.

Anybody knew about this?

Regards,
Juan Dent

[jlb]

Did you #include the chrono header file?

[JLBorges]

#include <chrono>

namespace X
{
    using namespace std ;
}

void foo()
{
    using namespace std::chrono ;

    X::chrono::hours a(1) ; // look up 'chrono::hours' in namespace ::X => look up in namespace ::std

    std::chrono::hours b(2) ; // look up 'std::chrono::hours' in namespace ::

    hours c(3) ; // look up 'hours' in namespace ::std::chrono (using namespace std::chrono)
}

[JUAN DENT]

Yes I had included chrono.

Yes JLBorges, you provide the rationale: X::chrono::hours implies lookup 'chrono::hours' in namespace ::X ==> look up in namespace ::std.

Interesting, yet a bit unexpected.

Thanks
Juan