flat_map and value_type

[gast128@…]

There is a problem with the value_type typedef. It is a typedef of std::pair<Key, Value> but shouldn't it be std::pair<const Key, Value>?

typedef boost::unordered_map<int, string> Int2StringUmap; typedef boost::container::flat_map<int, string> Int2StringFmap;

static_assert(std::is_same<Int2StringUmap::value_type, std::pair<const int, string>>::value, ""); ok static_assert(std::is_same<Int2StringFmap::value_type, std::pair<const int, string>>::value, ""); not ok

Maybe already reported, but I couldn't find it in the svn.

[Ion Gaztañaga]

Reviewing old bugs.

value_type is pair<Key,Value> as the internal type must be move constructible. This design is used since the pre-boost Loki AssocVector associative container.

[gast128@…]

Ok I have to work around this then, e.g. the following code will not compile when fed with a flat_map const_iterator:

template <typename Iterator>
struct key_iterator : public boost::bidirectional_iterator_helper<key_iterator<Iterator>, typename std::iterator_traits<Iterator>::value_type::first_type>
{
   typedef typename base::value_type value_type;


    value_type& operator* () const
    {
        return m_it->first;
    }

private:
    Iterator m_it;
};