Re: std::iter_swap and proxies

From:

"Igor Tandetnik" <itandetnik@mvps.org>

Newsgroups:

microsoft.public.vc.stl

Date:

Mon, 25 May 2009 10:36:09 -0400

Message-ID:

<OC93rYU3JHA.140@TK2MSFTNGP03.phx.gbl>

"Mycroft Holmes" <m.holmes@nospam.it> wrote in message
news:Oc7nAgS3JHA.1096@TK2MSFTNGP06.phx.gbl

we are testing some stl-compliant containers that have iterators on
bits (as vector<bool>)

This is an oxymoron. STL-compliant containers cannot have iterators on
bits. In particular, vector<bool> does not meet container requirements.
For more details, see

http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#96
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/1999/n1185.pdf
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2160.html

in visual studio 200x, iter_swap(i,j) performs swap(*i, *j).

See http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#187

but if *i is a proxy and not a real reference, this does not work

.... because i is not a forward iterator. See 24.1.3 table 74, which
requires that *i return a T&, where T is the value_type of the iterator.

Obviously we had to specialize std::swap for CONST PROXY_T&, but we
have the vague feeling that this could be avoided. any comments?

If you could specialize swap for your proxies, can't you also specialize
iter_swap for your "iterators"?
--
With best wishes,
Igor Tandetnik

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