Subject: [boost] [mpl] Using transform problem and solution
From: Edward Diener (eldiener_at_[hidden])
Date: 2011-01-27 21:04:54
I have a boost::mpl::vector of nullary metafunctions and I need to
transform it into a sequence of the metafunction's inner types. As in:
typedef boost::mpl::vector<boost::mpl::identity<int> > tvec;
typedef boost::mpl::vector<int> tvecinner;
So I try boost::mpl::transform:
typedef typename boost::mpl::transform<tvec,_1>::type ttrans;
But that does not work and the assert fails. Evidently my _1 is not
working by itself although it seems as if it should because it is a
placeholder expression and its inner type is what I want.
So I try:
template <class T>
struct tself : T
and now instead:
typedef typename boost::mpl::transform<tvec,tself<_1> >::type ttrans;
works fine and the assert succeeds.
But that 'tself' hack seems like it should be really unnecessary. Have I
missed something cleaner and easier ?
Boost list run by bdawes at acm.org, gregod at cs.rpi.edu, cpdaniel at pacbell.net, john at johnmaddock.co.uk