Re: [boost] Boost MPL metafunction shortcut

Subject: Re: [boost] Boost MPL metafunction shortcut
From: Dave Abrahams (dave_at_[hidden])
Date: 2011-04-09 17:21:40

At Sat, 09 Apr 2011 21:48:57 +0200,
Joel Falcou wrote:
> 
> I was thinking lately that it is a shame we can't do the following :
> 
> boost::mpl::transform< SomeSequence, _1&>
> 
> instead of the lengthy
> 
> boost::mpl::transform< SomeSequence, add_reference<_1> >
> 
> same goes for *, const, volatile :
> 
> boost::mpl::transform< SomeSequence, volatile _1**&>
> 
> Could it be possible to get such a behavior in MPL by having a pass of
> replacing type qualifier
> by corresponding metafunction until none are left then apply the lambda ?
> 
> In the same vein, having a MPL trandform turning a sequence of
> std::vector into their corresponding value_type
> require out of line small metafunction to be written. I guess a macro like
> 
> BOOST_MPL_ADAPTED_PLACEHOLDER( v,
> (type)(value_type)(reference)(const_reference) )
> 
> builds a whoel familly of _v1, ..., _v5 placeholder which behaves like
> _n and expose typedef
> called value_type etc ... that resolve to said small lambda function
> directly.
> 
> This would allow for a terse:
> 
> boost::mpl::transform< SomeSequence, _v1::reference>
> 
> Are these ideas out of the question due to some internals of MPL I
> missed ? Are they worthy a patch ?

They sound like great ideas to me.  Aleksey?

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com