c++ - Is it bad style to overload operators on std containers in global scope? -


i had problem arise:

// a.h #include <vector> typedef std::vector<unsigned char> buffer; buffer &operator+=(buffer &a, buffer const &b); 
// b.h namespace bar {      struct qux { };      qux &operator+=(qux &a, qux const &b); } 
// foo.cpp #include "a.h" #include "b.h"      // comment out, error goes away  namespace bar {     void foo()     {         buffer a, b;         += b;       // error     }  }

the problem (as described here) a += b; fails compile because bar::operator+=(qux&, qux const &) hides ::operator+=; , adl not find ::operator+ because adl searches namespace std; in case.

this icky because problem appears if b.h included -- b.h apparently has nothing buffer . code shouldn't break depending on whether include header.

(actually discovered when changing compilers, previous compiler using did name lookup incorrectly , accepted code).

my question is: overload in a.h bad idea because of issue?

i work around issue having b.h using ::operator+=; inside namespace bar seems pretty hacky, there better option?

the easiest, safest, reusable approach can think of have 1 of += arguments of type in operator's namespace:

template <typename t> struct argumentref {     argumentref(t& t) : t_(t) { }     operator t&() { return t_; }     operator const t&() const { return t_; }     t& t_; };  typedef std::vector<unsigned char> buffer; buffer &operator+=(argumentref<buffer> a, buffer const &b) { }

that said, inheritance - while controversial in c++ circles due non-virtual destructor in vector - fine imho, if aren't exposing buffer in api wider use, , not using dynamically allocated instances in code designed own , handle base class.


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