View Compilation Error

0_0_32807284_1208.cpp:36:8: error: specialization of 'template<class _Tp> struct std::hash' in different namespace [-fpermissive]
 struct hash<Data>
        ^
In file included from GCC4.9.2/x86_64-w64-mingw32/include/c++/bits/basic_string.h:3068:0,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/string:52,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/stdexcept:39,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/array:38,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/tuple:39,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/unordered_map:41,
                 from 0_0_32807284_1208.cpp:1:
GCC4.9.2/x86_64-w64-mingw32/include/c++/bits/functional_hash.h:58:12: error:   from definition of 'template<class _Tp> struct std::hash' [-fpermissive]
     struct hash;
            ^