[boost] Re: best way to make {reverse_}fold a sequence

From: Larry Evans (cppljevans_at_[hidden])
Date: 2005-02-28 11:27:47

On 02/28/2005 07:16 AM, David Abrahams wrote:
[snip]
>>OTOH, I really should have said "make the result of a fold metafunction
>>invokation into a sequence".  Would that have been sufficient to make
>>my meaning clear?
> 
> 
> Not really.  As I said, "fold and reverse_fold don't even have to
> _return_ sequences."  By that I mean that the result of invoking fold
> might be, e.g. int.

OK, granted, but I need it to be a sequence.  I guess what I planned
will not work on all results of fold, but it will work on at least some.
Right now, I'm just trying to get it to work on what I need at the
moment, which is part of a test driver.  I guess I'll just write
my own begin<fold<Sequence,StartState,ForwardOp> > and put it in
my test driver directory.

[snip]
>>
>>OTOH, I haven't really looked at fusion, so maybe I should.  It's
>>just I've found mpl very good and I've gotten used to it; hence,
>>I'm reluctant to change.  
> 
> 
> It's not a change.  Fusion is a compatible layer on top of MPL.
> 

My other post mentioned visitors.hpp and its need for fold.
How could fusion's tuple be used to implement visitors where
the critical need is a StartState superclass for all instantiations
of ForwardOp?