Re: [boost] [mpl, fusion] minimal conforming sequence

From: Peter Dimov (pdimov_at_[hidden])
Date: 2008-08-22 18:55:22

David Abrahams:
> on Wed Aug 20 2008, "Peter Dimov" <pdimov-AT-pdimov.com> wrote:
>
>> Hi,
>>
>> Assume that I have a custom type sequence S that has two operations,
>> size<S>::value and element<S,I>::type (with whatever spelling).
>>
>> What needs to be done to adapt S into a conforming MPL or Fusion 
>> sequence?
>>
>> In a perfect world, the answer would not require the inclusion any MPL
>> or Fusion headers and would consist of three specializations. ;-)
>
> Well, if it's an MPL sequence it's a fusion sequence, IIUC.  So you need
> to decide which sequence to model
> http://www.boost.org/doc/libs/1_36_0/libs/mpl/doc/refmanual/concepts.html

My original S is a random access sequence, so I'd probably want to model 
that.

> According to
> http://www.boost.org/doc/libs/1_36_0/libs/mpl/doc/refmanual/forward-sequence.html
> you can make a forward sequence with 5 specializations.

That's manageable, but I'd need a random access iterator first. An integral 
constant, too, if I really don't want to include an MPL header. It would've 
been nice if I could just point MPL to size<> and element<> and tell it to 
build the rest of the required boilerplate. Patches welcome, you say? :-)