Re: [RFC] add push/pop pragma to control the scope of "using"

[Marc Glisse]

On Wed, 15 Jan 2020, 马江 wrote:

Hello,
 After  some google, I find there is no way to control the scope of
"using" for the moment.  This seems strange as we definitely need this
feature especially when writing inline member functions in c++
headers.
 Currently I am trying to build a simple class in a c++ header file
as following:

#include <string>
using namespace std;
class mytest
{
 string test_name;
 int test_val;
public:
 inline string & get_name () {return test_name;}
};

Why is mytest in the global namespace?

 As a experienced  C coder, I know that inline functions must be put
into headers or else users could only rely on LTO. And I know that to
use "using" in a header file is a bad idea as it might silently change
meanings of other codes. However, after I put all my inline functions
into the header file, I found I must write many "std::string" instead
of "string" which is totally a torture.
 Can we add something like "#pragma push_using"  (just like #pragma
pop_macro)? I believe it's feasible and probably not hard to
implement.

We try to avoid extensions in gcc, you may want to propose this to the C++ 
standard committee first. However, you should first check if modules 
(C++20) affect the issue.

--
Marc Glisse