Associative container mapper example

[matpen]

I am experimenting with the new associative_container_view, which I find great. Now trying to "map" non-STL types in order to use them with RTTR, but the documentation is still sketchy.

Since no example is provided, I put together one here for Qt's QHash. I think I got pretty close to the "working" implementation, but it still crashes in some cases. I could use some help in debugging this. If found suitable, I would be glad to see it included in the docs.

[acki-m]

I will check this now.

[matpen]

Thank you very much!

[acki-m]

Unfortunately QHash is not fully STL compatible from the interface.
Just for now use this specialization. Remark I have not fully test it.
You don't have to reimplement every function, because you derive from detail::associative_container_base

namespace rttr
{

template<typename K, typename T, typename...Args>
struct associative_container_mapper<QHash<K, T>, Args...> : detail::associative_container_base<QHash<K, T>, Args...>
{
    static variant get_key(const detail::iterator_data& itr)
    {
        using itr_type = typename detail::associative_container_base<QHash<K, T>, Args...>::iterator;
        auto& it = iterator_wrapper_base<itr_type>::get_iterator(itr);
        return variant(std::ref(it.key()));
    }

    static variant get_value(const detail::iterator_data& itr)
    {
        using itr_type = typename detail::associative_container_base<QHash<K, T>, Args...>::iterator;
        auto& it = iterator_wrapper_base<itr_type>::get_iterator(itr);
        return variant(std::ref(it.value()));
    }

    static std::size_t erase(void* container, argument& key)
    {
        using key_type = typename detail::associative_container_base<QHash<K, T>, Args...>::key_t;
        if (key.get_type() == ::rttr::type::get<key_type>())
        {
            return reinterpret_cast<QHash<K, T>*>(container)->remove(key.get_value<key_type>());
        }
        else
        {
            return 0;
        }
    }

    static bool insert_key(void* container, argument& key, detail::iterator_data& itr)
    {
        return false;
    }

    static bool insert_key_value(void* container, argument& key, argument& value, detail::iterator_data& itr)
    {
        if (key.get_type() != ::rttr::type::get<K>() || value.get_type() != ::rttr::type::get<T>())
            return false;

        auto result_itr = reinterpret_cast<QHash<K, T>*>(container)->insert(key.get_value<K>(), value.get_value<T>());
        associative_container_mapper<QHash<K, T>, Args...>::create(itr, result_itr);
        return true;
    }
};

}

What is missing here, is the handling of the constness of the container. You should not be able to remove or insert items in a const container.

I have to think about it, to make specialization more easily....
As usal, I am open for suggestion.

[matpen]

I run a few tests, and it seems to work flawlessly!

However, I had to change the functions get_key() and get_value() as follows (or I get the error get_iterator() is not defined):

auto& it = associative_container_mapper<QHash<K, T>, Args...>::get_iterator(itr);
return variant(std::ref(it.key()));

Would you like me to provide a pull request which shows the working code as an example in the docs?

[acki-m]

Ahh I forgot the namespace detail:: Sorry. MSVC seems to be not that strict in this case.

Anyway, I working on a branch to get your custom types more easily into the mapper.
It requires on the implementation side one additional indirection, but it will make it much easier for you.
So, thanks for your offer, but I will adjust the code and will also provide a simple example. Stay tuned.

[matpen]

Ok, then. Thank you very much!
And great that you got an idea for an even easier solution!

[acki-m]

I am done. Please test it. There is also no additional drawback with my approach, actually I improved the performance a little bit.

REMARK
My changes will require code changes for everyone who has implemented some custom associative containers.

[matpen]

Beautiful! And much easier to implement.
According to my tests, everything works as expected: for QHash and QMap, I simply copy-pasted the example in the docs, and it worked out of the box. No other changes required to client code.

Thank you very much!