220 5869 <521C74C5.6060801@beamways.com> article
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From: Bengt Gustafsson <bengt.gustafsson@beamways.com>
Newsgroups: gmane.comp.lang.c++.isocpp.proposals
Subject: Re: Remove vector<bool>?
Date: Tue, 27 Aug 2013 11:43:33 +0200
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Zhihao Yuan skrev 2013-08-27 01:57:
> On Mon, Aug 26, 2013 at 7:22 PM, Howard Hinnant
> <howard.hinnant@gmail.com> wrote:
>> Question for Zhihao:
>>
>> Why does forward iterator's operator*() have to return a value_type& ?
>>
>> I'm well aware that this is what C++98/03/11 requires.  That's not what I'm asking.  I'm asking what is the benefit of this requirement in the C++1y context?  What problem does this requirement solve?
> Afaics, it makes the pointed object modifiable.  And move_iterator
> significantly benefits from it.  (Here is something I'm not sure:
> move_iterator requires only InputIterator, while dereferencing an
> InputIterator may return anything convertible to T -- is there anything
> broken here?)
>
No, he must be refering to something else, as the return value of 
vector<bool>::iterator::operator* does indeed make the pointed object 
modifiable.

I don't like when people speak in riddles to make other people feel like 
idiots! Please instead try to explain the issue at hand as clearly as 
you can.

The prime example I have been given of the badness of the vector<bool> 
specialization is that it does not have a .data() method. So be it, but 
in what case is using .data() preferred to using iterators?

The other problem was that some stl algorithms are very slow when the 
input iterators are for vector<bool>, but when I suggest a simple 
solution that would instead make them faster than their counterparts it 
is immediately shot down for not being orthogonal enough.

I don't really see the relevance of the argument that "anyone who needs 
a denser vector<bool> than the unspecialized one can always use 
bit_vector". This ASSUMES that programmers that make very simple use of 
a vector of bits aware of this new, later added class. At the same time 
the reason for getting rid of the specialized vector<bool> seems to be 
that we CAN'T ASSUME that programmers who are doing rather more complex 
programming know that vector<bool> is special, even though this is 
already pointed out in current textbooks.

I do think that the specialization was a mistake from the beginning, but 
I think that we should move on with an apology and concentrate on making 
it perform as expected from a packed representation, which requires the 
API I mentioned before. Also I think that the suggestion to remove it 
would never pass the committe scrutinization.

-- 

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