220 5860 <C114924A-C9F9-4F91-900C-C6CD6BBDA8B9@gmail.com> article
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From: Howard Hinnant <howard.hinnant@gmail.com>
Newsgroups: gmane.comp.lang.c++.isocpp.proposals
Subject: Re: Remove vector<bool>?
Date: Mon, 26 Aug 2013 21:06:37 -0400
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On Aug 26, 2013, at 8:58 PM, Zhihao Yuan <zy@miator.net> wrote:

> On Mon, Aug 26, 2013 at 8:36 PM, Howard Hinnant
> <howard.hinnant@gmail.com> wrote:
>> Bottom line:  All we have to do is stop assuming that *iter returns a va=
lue_type&.
>=20
> Conceptually agree.  And Stepanov's "Elements of Programming" 9.1
> has the same thought: Writability as an assignment to _sink_(x), while
> _sink_(x) is not necessarily a "real" reference to `x`.
>=20
> Ah, I see... We should be able to specialize iterator_traits to unblock
> proxy iterators...

And actually we already have done this for input iterators and output itera=
tors.  We just have this legacy requirement hanging around that forward ite=
rators (and bi and rand) must return a value_type& from operator*() (const =
value_type& for non-mutable variants).  The T& return from forward iterator=
 operator*() is kind of like dandelions.  It kind of looks pretty.  And it =
is very hard to get rid of. :-)  But I think we should make an effort to do=
 so.

libc++ is a working implementation where vector<bool>::[const_]iterator wor=
ks with everything in <algorithm>; some, but not enough of the algorithms a=
t greatly increased performance.  I.e. there is shipping implementation pra=
ctice to back up all of my hot air.  And we still need to deal with the fac=
t that vector<bool> has a terrible name.

Howard

--=20

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