Re: [Boost-users] Boost.mpl suggestion: variation of find_if

From: Vyacheslav Kononenko (groups_at_[hidden])
Date: 2005-06-14 21:36:04

--- Aleksey Gurtovoy <agurtovoy_at_[hidden]> wrote:

> Vyacheslav Kononenko writes:
> > I could not come with usable name for such thing
> but it could be
> > usable anyway.  So it is like find_if but applies
> a function to an
> > sequence and return first non void type that
> function returned. So
> > implementation would be trivial:
> >
> > template< typename Sequence, typename Func >
> > struct find_type : fold< Sequence, void_, if_<
> > is_void_< _1 >, Func< _2 >, _1 > {};
> 
> Or, which is likely to be more efficient,
> 
>     template< typename Seq, typename F > struct
> find_type
>     {
>         typedef typename find_if< 
>               transform_view<Seq,F>
>             , is_not_void_<_1>
>             >::type iter_;
> 
>         typedef typename eval_if< 
>               is_same< typename iter_::base,
> typename end<Seq>::type >
>             , void_
>             , deref<iter_>
>             >::type type;
>     };

Correct my if I am wrong but your will invoke F on
every element when mine will not.
 
> > If it can be implemented by current set of
> algorithms
> > please point me out.
> 
> Doesn't your sketch above employ an algorithm from
> the current set
> ('fold')? In any case, at the moment this feels too
> specialized to me
> to be considered for inclusion in the library. At
> the very least, it
> needs a name ;).

There is another topic about mpl for_each and I think
my algo would be usable there. But for the name it is
an author work to make names isn't it?
 
> -- 
> Aleksey Gurtovoy
> MetaCommunications Engineering
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