Proto for Boost mailing list page: Re: [proto] expanding Proto's library of callables

Subject: Re: [proto] expanding Proto's library of callables
From: Thomas Heller (thom.heller_at_[hidden])
Date: 2010-12-28 11:43:54

Eric Niebler wrote:

> On 12/28/2010 5:39 AM, Thomas Heller wrote:
>> I just saw that you added functional::at.
>> I was wondering about the rationale of your decision to make it a non
>> template.
>> My gut feeling would have been to have proto::functional::at<N>(seq)
>> and not proto::functional::at(seq, N).
> 
> Think of the case of Phoenix placeholders, where in the index is a
> parameter:
> 
>   when< terminal<placeholder<_> >, _at(_state, _value) >

vs:

when<terminal<placeholder<_> >, _at<_value>(_state)>

> For the times when the index is not a parameter, you can easily do:
> 
>   _at(_state, mpl::int_<N>())

vs:

_at<mpl::int_<N> >(_state)

just wondering ... the second version looks more "natural" and consistent