From: Chuck Allison (cda_at_[hidden])
Date: 2002-07-29 13:30:40
FWIW, the original bitstring proposal used operators pretty much exactly as
Victor described them (except < for proper subset, <= for subset). I like
the idea of having a full complement (sic) of set operations.
----- Original Message -----
From: "Jeremy Siek" <jsiek_at_[hidden]>
To: <boost_at_[hidden]>
Sent: Monday, July 29, 2002 12:11 PM
Subject: Re: [boost] dynamic_bitset request
>
> That's a good start. Why don't you finish fleshing this out in C++.
>
> BTW, it would be nice if I could implement this "set" interface for
> dynamic_bitset without conflicting with current operations. For example,
> operator<= is already taken to mean lexicographically less or equal.
> However, if that leads to too much ugliness, we can always go the adaptor
> route.
>
> Also, we'd probably want the combination assignment operators, such as |=
> and &= that are already in std::bitset and dynamic_bitset.
>
> Cheers,
> Jeremy
>
>
> On Mon, 29 Jul 2002, Victor A. Wagner, Jr. wrote:
> vawjr> It seems to me that if we're seriously going to consider adding
"set
> vawjr> semantics" to some set (pun intended) of classes; we could do a lot
worse
> vawjr> than look at a language that actually had set as part of its
fundamental
> vawjr> design (Pascal).
> vawjr>
> vawjr> IIRC Pascal (and I belive, Modula) sets supported the following
operators
> vawjr> -(unary) not (flip all truth elements in the set)
> vawjr> + union (C++ would probably use |)
> vawjr> * intersection (C++ would probably use &)
> vawjr> - difference .... a - b is equivalent to a * (-b)
> vawjr> xor(^) bit for bit ^
> vawjr> in set membership (usage: if y in myset then.....)
> vawjr> <= proper subset
> vawjr> >= proper superset
> vawjr> = equality (in C++ we use ==)
> vawjr> <> inequality (in C++ we use !=)
> vawjr>
> vawjr> all sets were "bounded" i.e. had a defined lower and upper bound of
> vawjr> possible members.
> vawjr>
> vawjr> IMO, there are good reasons to provide operators instead of just
standard
> vawjr> functions especially if an algebraic notation already exists for
the
> vawjr> concept. for example, it's a _lot_ easier to write
> vawjr>
> vawjr> a = b ^ c;
> vawjr>
> vawjr> than
> vawjr>
> vawjr> a.clear();
> vawjr> set_symmetric_difference(b.begin(), b.end(), c.begin(), c.end(),
> vawjr> back_inserter(a));
> vawjr> //or whatever one would have to write to get the equivalent of
> vawjr> back_inserter() for a set.
> vawjr>
> vawjr>
> vawjr> At Monday 2002/07/29 08:37, you wrote:
> vawjr> >Hi Dave,
> vawjr> >
> vawjr> >On Sat, 27 Jul 2002, David Abrahams wrote:
> vawjr> >dave> How about operator-() for set difference? That seems like an
obvious
> vawjr> >dave> need...
> vawjr> >
> vawjr> >One small problem with this is that one metaphor for
dynamic_bitset is
> vawjr> >that of a big integer. All the current operators are borrowed from
the
> vawjr> >builtin operators on an unsigned int. The problem is that
operator-
> vawjr> >doesn't mean set difference for unsigned int, but subtraction.
> vawjr> >
> vawjr> >One idea I've had in the past is to create a "Set" concept, which
would
> vawjr> >include things like union, difference, intersection, etc. For the
general
> vawjr> >idea of what the interface would look like, see:
> vawjr> >
> vawjr> >boost/graph/detail/set_adaptor.hpp
> vawjr> >
> vawjr> >Under this framework, it would make sense to implement this "Set"
> vawjr> >interface for dynamic_bitset, in addition to other classes that
can be
> vawjr> >thought of as implementing sets, such as std::set.
> vawjr> >
> vawjr> >Cheers,
> vawjr> >Jeremy
> vawjr> >
> vawjr> >
> vawjr>
>----------------------------------------------------------------------
> vawjr> > Jeremy Siek
http://php.indiana.edu/~jsiek/
> vawjr> > Ph.D. Student, Indiana Univ. B'ton email: jsiek_at_[hidden]
> vawjr> > C++ Booster (http://www.boost.org) office phone: (812)
855-3608
> vawjr>
>----------------------------------------------------------------------
> vawjr> >
> vawjr> >
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> vawjr> Victor A. Wagner Jr. http://rudbek.com
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> ----------------------------------------------------------------------
> Jeremy Siek http://php.indiana.edu/~jsiek/
> Ph.D. Student, Indiana Univ. B'ton email: jsiek_at_[hidden]
> C++ Booster (http://www.boost.org) office phone: (812) 855-3608
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