Re: [Boost-users] [mpl] newbie question

From: David Abrahams (dave_at_[hidden])
Date: 2006-02-24 15:07:39

"Andy Little" <andy_at_[hidden]> writes:

> "David Abrahams" <dave_at_[hidden]> wrote in message
> news:ud5hcene3.fsf_at_boost-consulting.com...
>> "Andy Little" <andy_at_[hidden]> writes:
>>
>>> I shall continue to question whether it is the best design. I dont
>>> know whether there are plans to C++ standardise any of mpl , but I
>>> would certainly like to raise that and some other issues in that
>>> case.
>>
>> Question all you want as far as I'm concerned.  Until you can propose
>> a technically superior solution to the problem of sequence identity,
>> it won't make any difference, because the authors of MPL have already
>> tried, and failed, to find one.
>
> I am not concerned with the intractible problem of sequence identity
> ( whatever that means) at the moment.

Then what was this indictment about?

Me:
  > The result of the transform is only required to be "concept-identical"
  > to the result you're looking for.

You:
  IMO that behaviour is sloppy.

> What is the problem with the result of plus<int_<A>,int_<B>> being
> int_<A+B> ?

I don't know if there are any serious problems with it, but I'm
guessing it would mean the addition of a number of specializations,
and additional ugly workarounds to support broken compilers.  And, of
course, the bigger problem is that we don't have

    a. A patch implementing it
    b. Tests to verify that the patch worked
    c. Time to implement it ourselves right now

The extra code may or may not be an obstacle to inclusion.  I can't
speak for Aleksey, but I guess that to know, he'd have to see the
patch.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com