Re: [Boost-users] Odd limitation in Fusion design ?

Subject: Re: [Boost-users] Odd limitation in Fusion design ?
From: John Dlugosz (JDlugosz_at_[hidden])
Date: 2010-07-08 20:42:41

> > So you give it two functions, one to do on the way down and another
> to do on a the way up?
> >
> Yes.  However, I'm not sure if the way-up function is the NowUp or Else
> template parameter.  I'd have to look at the
> backus_turingaward_lecture.pdf reference to see which is which.
> 
> 

My own effort at this, straddling the compile-time and run-time boundaries, is posted on a new topic.  I can't get the necessarily run-time test for done-ness to play nice with the compile-time metafunctions that are "run" (expanded) regardless of what might happen at run time.

I'm sure it's a documentation problem with Fusion.  There is no guarantee that the 'end' iterator evaluates to a unique type that won't happen to match the iterator's type inside the normal work.  For a cons (Lisp-like) list I'm rather certain that it will be, unless he's using some kind of type erasure in the implementation, but I don't want to make that assumption, and even if that were taken, it seems difficult to accomplish (compared with simply knowing a simple name for a type that could be used in a partial specialization or overloaded form).  I'm assuming that there is intended to be some simple and natural way to iterate a collection other than using the canned fold or for_each functions!

--John







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