Function as_double

include/jsoncons/basic_json.hpp:3841–3849

        }

        double as_double() const
        {
            auto result = try_as_double();
            if (!result)
            {
                JSONCONS_THROW(conv_error(result.error().code()));
            }
            return *result;
        }

        template <typename T,typename Alloc, typename TempAlloc>
        typename std::enable_if<ext_traits::is_string<T>::value &&