How to "concatenate" boost::mpl::vectors

Question

I have to different vectors

mpl::vector<Type1, Type2...>
mpl::vector<Type3, Type4...>

I'd like to "concatenate" them to form:

mpl::vector<Type1, Type2, Type3, Type4...>

This would allow me to prepare vector templates and reuse them afterwards. There are different solutions to my problem, but this approach seems most appropriate to me.

Thanks...

Scaffolding

Answer 1

The libaray native supported function boost::mpl::joint_view is probably a better choice. It is optimized and lazy-evaluated.

http://www.boost.org/doc/libs/1_55_0/libs/mpl/doc/refmanual/joint-view.html

Soriano

Works like charm! And it does not explode the virtual memory, required for compilation. Thank you very much! – Scaffolding

Answer 2

Like this:

// include the appropriate headers
typedef mpl::vector<Type1, Type2> first_type;
typedef mpl::vector<Type3, Type4> second_type;
typedef mpl::copy<first_type::type, mpl::back_inserter<second_type> >::type concat_type;

Meltwater

I'm not sure, but I think that first_type and second_type are switched. If I'm not wrong with that you'll get vector<Type3,Type4,Type1,Type2>. – Cabin

@cv_and_he Right, I just didn't give importance to the types' order. – Meltwater

Thanks, this code does the job. Though in my case this method consumes a huge amount of memory at compile time... – Scaffolding

@Scaffolding well, template metaprogramming requires a lot of ct-resources, especially with MSVC. – Meltwater

Answer 3

You can use mpl::copy, which uses mpl::fold internally.

typedef mpl::vector<T0, T1> s0;
typedef mpl::vector<T2, T3> s1;
typedef mpl::copy<
    s1,
    mpl::back_inserter<s0>
>::type concatenated;

BOOST_MPL_ASSERT((
    mpl::equal<
        concatenated,
        mpl::vector<T0, T1, T2, T3>
    >
));

Moujik