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Subject: [boost] Boost MPL metafunction shortcut
From: Joel Falcou (joel.falcou_at_[hidden])
Date: 2011-04-09 15:48:57

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

(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

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 ?

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