Boost logo

Boost :

Subject: Re: [boost] [GSoC][MPL11] Post C++Now update
From: Larry Evans (cppljevans_at_[hidden])
Date: 2014-05-21 12:42:27

On 05/20/14 17:00, Roland Bock wrote:
> On 2014-05-20 20:59, Larry Evans wrote:
>> On 05/18/14 15:41, Louis Dionne wrote:
>>> Dear Boost,
>>> A lot happened during the past week in Aspen; the goal of this message
>>> is to summarize insights, changes and feedback received wrt MPL11.
>>> The slides of the presentation are available at [1]. The second part of
>>> the presentation is especially relevant to get an overview of the
>>> designs
>>> considered so far.
>>> Merging the MPL and Fusion
>>> --------------------------
>>> After discussing the issue several times during the week, I (and others)
>>> think it might be possible to merge Fusion and the MPL into a single
>>> library. I am currently trying to write a library that does that. Since
>>> this constitutes a large reorientation, I created a new repository which
>>> is available at [2]. Those with interest should consider subscribing to
>>> the repository to be updated as I make progress.
>>> Iterator-free design
>>> --------------------
>>> I was a bit anxious that people would complain about this, but the
>>> contrary
>>> happened. Nobody complained and some people expressed support. This
>>> design
>>> aspect will stay as-is.
>>> Request for guinea pigs
>>> -----------------------
>>> I am looking for people with hardcore C++1y metaprogramming needs who
>>> will
>>> be willing to test the library I come up with (MPL11 or MPL + Fusion
>>> merge).
>>> I also need to see use cases for the library, so please reply even if
>>> you
>>> are not willing to test.
>> As mentioned in this post:
>> One use case is:
>>> 3) A guaranteed non-recursive way to access elements of parameter
>>> packs
>> and Doug Gregor (quoting from above post) says:
>> This is probably the most-requested feature for variadic templates,
>> and it never it made it because we never found a good, unambiguous
>> syntax.
>> The attached seems to do that. What about adding something
>> like this to the library?
>> -regards,
>> Larry
> Attached is a solution that uses C++14 index sequence (which is
> recursive, afaik), but is otherwise recursion free. Maybe there is a
> non-recursive alternative to index_sequence to "eat up" the first N-1
> elements?
> The code based on the third attachment of this clang bug report
> Regards,
> Roland
Thanks very much Roland. I had no idea there was this way
to do it. However, I had a lot of trouble understanding
how it worked; hence, I added a bunch of comments, as shown
in the attached. After adding the comments, I now understand
what you mean by "eat up" the first N-1 elements.


Boost list run by bdawes at, gregod at, cpdaniel at, john at