Importing std::tr1 into std - is it legal? Does it improve portability?
c++, compatibility, tr1
Solution
You should not touch the `std` namespace: even if it works now, it can cause severe headaches later (with a new version of the compiler, on a different compiler, etc).
Update: Quote from the standard (C++ 2003, Section 17.4.3.1 "Reserved names") (found here):
It is undefined for a C++ program to add declarations or definitions to namespace std or namespaces within namespace std unless otherwise specified. A program may add template specializations for any standard library template to namespace std. Such a specialization (complete or partial) of a standard library template results in undefined behavior unless the declaration depends on a user-defined type of external linkage and unless the specialization meets the standard library requirements for the original template. [emphasis mine]
Problem
I have C++03 code that looks like this: ``` #include <boost/tr1/unordered_map.hpp> ... std::tr1::unordered_map<std::string, int> mystuff; ... ``` I started to wonder that i would suffer later if/when i convert my code to C++11, which (i guess) doesn't have `std::tr1::unordered_map` but has `std::unordered_map` instead. So i came up with the following hack: ``` namespace std { using namespace ::std::tr1; } ... std::unordered_map<std::string, int> mystuff; // no tr1 now! ... ``` Is it legal (maybe importing stuff into `std` is forbidden)? Will it make it easier to port/interoperate with C++11 code?