is_map_like

`is_map_like`

Determine if T can be treated like a 1-to-1 mapping during conversions.

template<
    class T>
struct is_map_like;

Given t, a glvalue of type T, if

is_sequence_like<T>::value is true; and
given type It denoting decltype(std::begin(t)), and types K and M, std::iterator_traits<It>::value_type denotes std::pair<K, M>; and
std::is_string_like<K>::value is true; and
given v, a glvalue of type V, and E, the type denoted by decltype(t.emplace(v)), std::is_tuple_like<E>::value is true;

then the trait provides the member constant value that is equal to true. Otherwise, value is equal to false.

Users can specialize the trait for their own types if they don’t want them to be treated like mappings. For example:

namespace boost {
namespace json {

template <>
struct is_map_like<your::map> : std::false_type
{ };

} // namespace boost
} // namespace json

The restriction for t.emplace() return type ensures that the container does not accept duplicate keys.