Re: [boost] (infinite) sequences using recurrence relations

From: John E. Potter (jpotter_at_[hidden])
Date: 2001-08-10 13:17:39

On Fri, 10 Aug 2001, Corwin Joy wrote:

> Still, the way the standard
> defines equality for
> input iterator bugs me then since it seems to me that if (i, j) is not in
> the domain of == the operator
> should return false rather than returning true just because (i, j) point to
> the same stream.

Err, if (i, j) is not in the domain of ==, your computer should catch
fire when you test it.

Operator== is an equivalence relation.  For istream_iterators, not
input iterators in general, the domain is iterators into a stream
and the end of stream iterator.  The equalalence classes are the
end of stream iterator and other streams iterator.  For istreambuf
iterators, there are only two equivalence classes.  IMO, that is
overspecified.  Algorithms operate on iterator ranges.  The only
requirement from the algorithms is that two end of stream iterators
compare equal and that a non end of stream iterator not compare
equal to an end of stream iterator.  There is no use for a comparison
of two non end input iterators.

John