Re: [boost] [type_at] Variadic template utility

Subject: Re: [boost] [type_at] Variadic template utility
From: Larry Evans (cppljevans_at_[hidden])
Date: 2011-05-26 07:19:50

On 05/26/11 04:47, tymofey wrote:
>> Robert Jones <robertgbjones_at_[hidden]>
>> On Thu, May 26, 2011 at 8:34 AM, tymofey <tymofey_at_[hidden]> wrote:
>>
>>> While experimenting with varidic templates of the upcoming standard i
>>> discovered that quite often one would need to extract a type from parameter
>>> pack at specified position. 
[snip]
>> Forgive me if I'm missing the point, but isn't this essentially Boost.MPL's
>> 'at' metafunction?
>>
>> - Rob.
> 
> It is, but without the need to drag in mpl::vector with the limitations it imposes.
> 
Could you please describe those limitations, other than the one for
maximum arity, which, IIUC, is modifiable by redefining the macro:

  BOOST_MPL_LIMIT_VECTOR_SIZE

?  Also, IIUC, one reason for using the macro, and the preprocessor,
is to speed compile time by reducing the number of template
instantiations. Thus, maybe one advantage of mpl::at vs your type_at
is compile time. You might check that somehow.

-regards,
Larry