c++11 - g++4.9.2 and rvalue reference maps -

so, have following code:

#include <map> #include <string> #include <iostream>  struct mockmapitem {     std::string property;      mockmapitem(const std::string& value) : property(value) {         std::cout << "constructed mockmapitem string!" << std::endl;      } };  typedef typename std::map<std::string, const mockmapitem&& > itemmap;  int main() {     mockmapitem map_item("some string value");      itemmap themap;     themap.emplace("something", std::move(map_item));  } 

for ease of access, have put here:

http://coliru.stacked-crooked.com/a/7e80bc37d904510d

and here:

http://ideone.com/2wkomc

now comes fun:

the coliru site compiles , runs it.

the ideone 1 gives following error:

compilation error   time: 0 memory: 0 signal:0  prog.cpp:14:60: error: template argument 2 invalid  typedef typename std::map<std::string, const mockmapitem&& > itemmap;                                                         ^ prog.cpp:14:60: error: template argument 4 invalid prog.cpp:14:62: error: 'itemmap' in namespace 'std' not name type  typedef typename std::map<std::string, const mockmapitem&& > itemmap; 

but can compile code, although using g++4.8.4 (and clang 3.4)...

and i'm wondering 1 right, , more why?

23.2.1 says container's value_type must erasable container, , 23.2.4 says maps , multimaps requirements apply key_type , mapped_type.

a reference type not erasable container, because cannot form pointer reference type , cannot destroy using allocator_traits::destroy (because allocators support non-const object types, , reference type not object type).

so const mockmapitem&& type fails meet requirements use in containers, , has undefined behaviour.

edit: in c++11 requirement in 23.2.1 value_type destructible, , reference type is destructible. maybe well-formed in c++11, not c++14. hmm.