GCC 8 20180204 prodces unexpected ambiguous overload error

[Bert Wesarg <bert.wesarg@xxxxxxxxxxxxxx>]

Dear all,

I encounter a compile error when using GCC 8 20180204 with a simple
C++ program which worked before. Even with GCC 8 20170923. I would
like to understand, why this does not compile anymore, and how to fix
it.

test-map.cc: In member function 'void
map_type_to_map<IdType>::add(const value_type&)':
test-map.cc:34:59: error: call of overloaded 'insert(std::map<int,
int>::const_iterator, std::map<int, int>::const_iterator)' is
ambiguous
         current_values.insert(values.begin(), values.end());
                                                           ^
In file included from /home/wesarg/opt/gcc-8-20180204/include/c++/8.0.1/map:61,
                 from test-map.cc:1:
/home/wesarg/opt/gcc-8-20180204/include/c++/8.0.1/bits/stl_map.h:876:2:
note: candidate: 'std::map<_Key, _Tp, _Compare, _Alloc>::iterator
std::map<_Key, _Tp, _Compare, _Alloc>::insert(std::map<_Key, _Tp,
_Compare, _Alloc>::const_iterator, _Pair&&) [with _Pair =
std::_Rb_tree_const_iterator<std::pair<const int, int> >;
<template-parameter-2-2> = <missing>; _Key = int; _Tp = int; _Compare
= std::less<int>; _Alloc = std::allocator<std::pair<const int, int>
>]'
  insert(const_iterator __position, _Pair&& __x)
  ^~~~~~
/home/wesarg/opt/gcc-8-20180204/include/c++/8.0.1/bits/stl_map.h:892:2:
note: candidate: 'void std::map<_Key, _Tp, _Compare,
_Alloc>::insert(_InputIterator, _InputIterator) [with _InputIterator =
std::_Rb_tree_const_iterator<std::pair<const int, int> >; _Key = int;
_Tp = int; _Compare = std::less<int>; _Alloc =
std::allocator<std::pair<const int, int> >]'
  insert(_InputIterator __first, _InputIterator __last)
  ^~~~~~


Thanks.

Best,
Bert

#include <map>

class map_int_to_map :
    private std::map<int, std::map<int, int>>
{
public:
    using value_type = std::map<int, int>;
    using base_type  = std::map<int, value_type>;

    map_int_to_map() : base_type() {}

    ~map_int_to_map() {}

    inline void add( const value_type& values ) {
        value_type current_values;
        current_values.insert( values.begin(), values.end() );
    }
};

template<typename IdType>
class map_type_to_map :
    private std::map<IdType, std::map<int, int>>
{
public:
    using value_type = std::map<int, int>;
    using base_type  = std::map<IdType, value_type>;

    map_type_to_map() : base_type() {}

    ~map_type_to_map() {}

    inline void add( const value_type& values ) {
        value_type current_values;
        current_values.insert(values.begin(), values.end());
    }
};

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