The interface of MetaobjectSequence

[matus-chochlik]

meta-ObjectSequence is a metaobject just like anything else with the following trivial operations:

get_size<meta-ObjectSequence> -> integral-constant
get_element<meta-ObjectSequence, Index> -> meta-Object

and the following operation for convenience:

template <ObjectSequence MoS, template <class> class Tpl>
struct unpack_sequence
{
    typedef Tpl<Mo0, Mo1, Mo2, ...> type;
};

Questions:

• Do we want to explicitly in the standard specify the complexity of the get_size and get_element operation or just have the compiler-vendors to do a best effort implementation.
• Do we want another interface, for example some-sort of compile-time forward iteration? Here I'd argue (from experience [1]) that such interface is quite clumsy to use especially with variadic templates.

[1] http://kifri.fri.uniza.sk/~chochlik/mirror-lib/html/doxygen/mirror/html/d2/d16/structmirror_1_1mp_1_1range.html

[ricardofandrade]

My $0.02:

• Best effort. Maybe just something like "at least O(N)".
• Indexed and pack seem sufficient. Iterating over variadic argument by being handled in other groups. If constexpr becomes supported directly, maybe unpacking to non-type template argument pack of metaobject_id constants.