Re: [Boost-users] [fusion][mpl][array] making boost array a conforming mpl sequence (through fusion)

Subject: Re: [Boost-users] [fusion][mpl][array] making boost array a conforming mpl sequence (through fusion)
From: Stjepan Rajko (stjepan.rajko_at_[hidden])
Date: 2009-02-11 01:16:53

On Tue, Feb 10, 2009 at 8:10 PM, Joel de Guzman
<joel_at_[hidden]> wrote:
> Stjepan Rajko wrote:
>>
>> Hi,
>>
>> I tried to make boost::array a conforming MPL sequence by including:
>>
>> #include <boost/fusion/adapted/array.hpp> // makes array a conforming
>> fusion sequence
>> #include <boost/fusion/mpl.hpp> // makes fusion sequences conforming
>> MPL sequences
>>
>> but,
>>
>> typedef boost::array<int, 1> array;
>> assert(boost::mpl::is_sequence<array>::type::value);  // fails
>>
>> Am I misinterpreting the fusion documentation in expecting that this
>> should work?  Is there another way of making boost::array an mpl
>> sequence?
>
> I think the basic problem is that is_sequence is not really part
> of the requirements for an MPL sequence. You don't have to be a
> conforming MPL sequences. I am not sure how to best approach this.
> Perhaps the MPL authors have a better idea?
>

Joel, thanks for your response.

My original problem was with a simple application of mpl::transform,
which produced an error stating:
no class template named 'apply' in 'struct
boost::mpl::clear_impl<boost::mpl::non_sequence_tag>

The above code was just an attempt at a minimal example.  Also, the
same above code passes if boost::array<int, 1> is replaced with
fusion::vector<int>, so my impression is that there is something
happening for fusion-proper sequences that is not happening for the
adapted array.

I can provide a minimal example that involves mpl::transform if that
is helpful, but I imagine (perhaps erroneously) that whatever fixes
mpl::is_sequence would also fix my problem with mpl::transform.

Stjepan