operator[] does not compile with non-POD value type.

[tjcbs]

On VS2015:

#include <string>
#include "robin_hood.h"

int main()
{
    robin_hood::unordered_flat_map<int, std::string> map;
    map[1] = "bug?";
}

Produces:

1>c:\projects\test\robin_hood.h(607): error C2476: 'constexpr' constructor does not initialize all members
1>  c:\projects\test\robin_hood.h(642): note: 'robin_hood::pair<int,T>::first' was not initialized by the constructor
1>          with
1>          [
1>              T=std::string
1>          ]
1>  c:\projects\test\robin_hood.h(643): note: 'robin_hood::pair<int,T>::second' was not initialized by the constructor
1>          with
1>          [
1>              T=std::string
1>          ]
1>  c:\projects\test\robin_hood.h(918): note: see reference to function template instantiation 'robin_hood::pair<int,T>::pair<_Ty&&,>(std::piecewise_construct_t,std::tuple<_Ty &&>,std::tuple<>) noexcept' being compiled
1>          with
1>          [
1>              T=std::string,
1>              _Ty=int
1>          ]
1>  c:\projects\test\robin_hood.h(918): note: see reference to function template instantiation 'robin_hood::pair<int,T>::pair<_Ty&&,>(std::piecewise_construct_t,std::tuple<_Ty &&>,std::tuple<>) noexcept' being compiled
1>          with
1>          [
1>              T=std::string,
1>              _Ty=int
1>          ]
1>  c:\projects\test\robin_hood.h(2026): note: see reference to function template instantiation 'robin_hood::detail::Table<true,80,Key,T,Hash,KeyEqual>::DataNode<robin_hood::detail::Table<true,80,Key,T,Hash,KeyEqual>,true>::DataNode<const std::piecewise_construct_t&,std::tuple<_Ty &&>,std::tuple<>>(M &,const std::piecewise_construct_t &,std::tuple<_Ty &&> &&,std::tuple<> &&) noexcept' being compiled
1>          with
1>          [
1>              Key=int,
1>              T=std::string,
1>              Hash=robin_hood::hash<int>,
1>              KeyEqual=std::equal_to<int>,
1>              _Ty=int,
1>              M=robin_hood::detail::Table<true,80,int,std::string,robin_hood::hash<int>,std::equal_to<int>>
1>          ]
1>  c:\projects\test\robin_hood.h(2025): note: see reference to function template instantiation 'robin_hood::detail::Table<true,80,Key,T,Hash,KeyEqual>::DataNode<robin_hood::detail::Table<true,80,Key,T,Hash,KeyEqual>,true>::DataNode<const std::piecewise_construct_t&,std::tuple<_Ty &&>,std::tuple<>>(M &,const std::piecewise_construct_t &,std::tuple<_Ty &&> &&,std::tuple<> &&) noexcept' being compiled
1>          with
1>          [
1>              Key=int,
1>              T=std::string,
1>              Hash=robin_hood::hash<int>,
1>              KeyEqual=std::equal_to<int>,
1>              _Ty=int,
1>              M=robin_hood::detail::Table<true,80,int,std::string,robin_hood::hash<int>,std::equal_to<int>>
1>          ]
1>  c:\projects\test\robin_hood.h(1643): note: see reference to function template instantiation 'std::basic_string<char,std::char_traits<char>,std::allocator<char>> &robin_hood::detail::Table<true,80,Key,T,Hash,KeyEqual>::doCreateByKey<int,std::basic_string<char,std::char_traits<char>,std::allocator<char>>>(Arg &&)' being compiled
1>          with
1>          [
1>              Key=int,
1>              T=std::string,
1>              Hash=robin_hood::hash<int>,
1>              KeyEqual=std::equal_to<int>,
1>              Arg=int
1>          ]
1>  c:\projects\test\robin_hood.h(1643): note: see reference to function template instantiation 'std::basic_string<char,std::char_traits<char>,std::allocator<char>> &robin_hood::detail::Table<true,80,Key,T,Hash,KeyEqual>::doCreateByKey<int,std::basic_string<char,std::char_traits<char>,std::allocator<char>>>(Arg &&)' being compiled
1>          with
1>          [
1>              Key=int,
1>              T=std::string,
1>              Hash=robin_hood::hash<int>,
1>              KeyEqual=std::equal_to<int>,
1>              Arg=int
1>          ]
1>  c:\projects\test\test.cpp(10): note: see reference to function template instantiation 'std::basic_string<char,std::char_traits<char>,std::allocator<char>> &robin_hood::detail::Table<true,80,Key,T,Hash,KeyEqual>::operator []<std::basic_string<char,std::char_traits<char>,std::allocator<char>>>(int &&)' being compiled
1>          with
1>          [
1>              Key=int,
1>              T=std::string,
1>              Hash=robin_hood::hash<int>,
1>              KeyEqual=std::equal_to<int>
1>          ]
1>  c:\projects\test\test.cpp(10): note: see reference to function template instantiation 'std::basic_string<char,std::char_traits<char>,std::allocator<char>> &robin_hood::detail::Table<true,80,Key,T,Hash,KeyEqual>::operator []<std::basic_string<char,std::char_traits<char>,std::allocator<char>>>(int &&)' being compiled
1>          with
1>          [
1>              Key=int,
1>              T=std::string,
1>              Hash=robin_hood::hash<int>,
1>              KeyEqual=std::equal_to<int>
1>          ]

[martinus]

Looks like a VS2015 bug to me. Can't you use something more recent?