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Re: Anyone ever used vector<bool> ?

From "Alf P. Steinbach" <alf.p.steinbach@gmail.com>
Newsgroups comp.lang.c++
Subject Re: Anyone ever used vector<bool> ?
Date 2022-05-07 19:12 +0200
Organization A noiseless patient Spider
Message-ID <t569al$2hp$1@dont-email.me> (permalink)
References (11 earlier) <87sfpn7wz2.fsf@bsb.me.uk> <t534c8$c7b$1@dont-email.me> <t53lh5$rv8$1@dont-email.me> <t53vrg$fvm$1@dont-email.me> <t567nn$kdf$1@dont-email.me>

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On 7 May 2022 18:45, Andrey Tarasevich wrote:
> On 5/6/2022 1:18 PM, Alf P. Steinbach wrote:
>> On 6 May 2022 19:22, Andrey Tarasevich wrote:
>>> On 5/6/2022 5:29 AM, Alf P. Steinbach wrote:
>>>> On 6 May 2022 12:54, Ben wrote:
>>>>>
>>>>>> The academic idealists won, the practically oriented people lost, and
>>>>>> `std::list` became useless.
>>>>>
>>>>> Curious that you put it like that.  There doesn't seem to be anything
>>>>> obviously idealistic in opting for O(1) size and linear splicing for
>>>>> "foreign" sub-lists.  I don't recall ever wanting that form of splice,
>>>>> so I would consider C++'s choice quite practical (for me).  What makes
>>>>> this the "idealists" preferred option?
>>>>
>>>> E.g. as Howard Hinnant put it some time before C++11, in an article at
>>>> <url: https://howardhinnant.github.io/On_list_size.html>:
>>>>
>>>> ❝As the standard is written today, none of the containers are 
>>>> required to have an O(1) size(). I believe that this should be 
>>>> corrected in C++0X. [Expressing an academic ideal:] If a container 
>>>> has a size() member, it should be required to have O(1) complexity. 
>>>> [Again expressing an academic ideal:] If a container can not manage 
>>>> this, it should not have a size() member at all. Clients can always 
>>>> compute distance(begin(),end()).❞
>>>>
>>>> The inline square brackets notes are my annotations.
>>>
>>>
>>> The quoted text actually makes an extremely good and logical point. 
>>> This is exactly why we have such "red flag" functions as 
>>> `std::distance` and `std::advance` in standard library: as 
>>> deliberately conspicuous indicators of potentially inefficient 
>>> temporary/stub/niche code.
>>>
>>> If the objective were to keep `splice()` efficient, then removing 
>>> inefficient `size()` from `std::list<>` entirely and forcing the user 
>>> to use `std::distance` would have been an ideal solution. Beautiful 
>>> idea!
>>
>> No no no. A `std::list` with O(1) other list splice can in most cases 
>> of ordinary usage know its size, and it can keep track of whether it 
>> knows or this time needs to count. This is a near cost free 
>> optimization (relative to overhead of e.g. creating a node, with 
>> internal dynamic allocation) with great dividends, that I believe 
>> client code can't do.
> 
> Lazy evaluation of `size()` is a viable technique that nevertheless has 
> its own set of issues. It is an operation that is "logically const" but 
> not "physically const", since it has to updated its "size is known" 
> state.

Right, a reasonable C++11 implementation is a `mutable optional<Size>`, 
where `Size` is `ptrdiff_t`.


> In a single-threaded context it is viable, but cue in 
> multithreading considerations and it becomes problematic.

That as I see it erroneous conclusion appears to build on three invalid 
assumptions:

Assumption 1. Any `const` object of a standard library type is or should 
be safe for multithreading.
Assumption 2. It's impossible or impractical to let client code know if 
object is in mt-safe stable state.
Assumption 3: It's impossible or impractical for client code to force an 
mt-safe stable state.

In particular, a single call to `.size()` would suffice to bring the 
object to stable state so it could be shared for reading. Client code 
responsibility to do MT right, not `std::list` responsibility.

I failed to mention similar technique earlier for forcing a counting of 
the transferred nodes in a splice. With lazy size count one can just 
transfer them to a temporary empty list first; transferring all from 
that intermediate list then effects a count. That trick could be made 
unnecessary in the rare cases where needed, by adding an option to the 
splice function to count  --  which is about empowering client code, 
giving client code the choice, instead of forcing inefficiency on it.


Cheers,

- Alf

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Thread

Anyone ever used vector<bool> ? Muttley@dastardlyhq.com - 2022-05-03 15:16 +0000
  Re: Anyone ever used vector<bool> ? Ben <ben.usenet@bsb.me.uk> - 2022-05-03 16:39 +0100
    Re: Anyone ever used vector<bool> ? Muttley@dastardlyhq.com - 2022-05-03 16:12 +0000
      Re: Anyone ever used vector<bool> ? Bo Persson <bo@bo-persson.se> - 2022-05-03 20:25 +0200
        Re: Anyone ever used vector<bool> ? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-05-03 12:00 -0700
        Re: Anyone ever used vector<bool> ? Juha Nieminen <nospam@thanks.invalid> - 2022-05-04 10:50 +0000
  Re: Anyone ever used vector<bool> ? Muttley@dastardlyhq.com - 2022-05-03 16:14 +0000
  Re: Anyone ever used vector<bool> ? Jack Lemmon <invalid@invalid.net> - 2022-05-03 17:33 +0100
    Re: Anyone ever used vector<bool> ? Manfred <noname@add.invalid> - 2022-05-03 19:13 +0200
      Re: Anyone ever used vector<bool> ? Muttley@dastardlyhq.com - 2022-05-04 09:13 +0000
    Re: Anyone ever used vector<bool> ? Juha Nieminen <nospam@thanks.invalid> - 2022-05-04 10:45 +0000
      Re: Anyone ever used vector<bool> ? Paavo Helde <eesnimi@osa.pri.ee> - 2022-05-04 14:09 +0300
        Re: Anyone ever used vector<bool> ? Frederick Virchanza Gotham <cauldwell.thomas@gmail.com> - 2022-05-04 14:39 -0700
          Re: Anyone ever used vector<bool> ? red floyd <no.spam.here@its.invalid> - 2022-05-04 15:17 -0700
            Re: Anyone ever used vector<bool> ? James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-05-05 01:57 -0400
          Re: Anyone ever used vector<bool> ? Paavo Helde <eesnimi@osa.pri.ee> - 2022-05-05 09:12 +0300
        Re: Anyone ever used vector<bool> ? Juha Nieminen <nospam@thanks.invalid> - 2022-05-05 06:17 +0000
          Re: Anyone ever used vector<bool> ? Ben <ben.usenet@bsb.me.uk> - 2022-05-05 10:49 +0100
            Re: Anyone ever used vector<bool> ? Öö Tiib <ootiib@hot.ee> - 2022-05-05 04:29 -0700
              Re: Anyone ever used vector<bool> ? Ben <ben.usenet@bsb.me.uk> - 2022-05-05 12:56 +0100
                Re: Anyone ever used vector<bool> ? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-05-05 21:37 +0200
                Re: Anyone ever used vector<bool> ? Ben <ben.usenet@bsb.me.uk> - 2022-05-05 21:13 +0100
                Re: Anyone ever used vector<bool> ? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-05-06 10:39 +0200
                Re: Anyone ever used vector<bool> ? Ben <ben.usenet@bsb.me.uk> - 2022-05-06 11:54 +0100
                Re: Anyone ever used vector<bool> ? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-05-06 14:29 +0200
                Re: Anyone ever used vector<bool> ? Ben <ben.usenet@bsb.me.uk> - 2022-05-06 17:05 +0100
                Re: Anyone ever used vector<bool> ? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-05-06 10:22 -0700
                Re: Anyone ever used vector<bool> ? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-05-06 22:18 +0200
                Re: Anyone ever used vector<bool> ? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-05-06 13:51 -0700
                Re: Anyone ever used vector<bool> ? Muttley@dastardlyhq.com - 2022-05-07 08:41 +0000
                Re: Anyone ever used vector<bool> ? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-05-07 12:33 +0200
                Re: Anyone ever used vector<bool> ? Muttley@dastardlyhq.com - 2022-05-07 16:12 +0000
                Re: Anyone ever used vector<bool> ? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-05-07 09:37 -0700
                Re: Anyone ever used vector<bool> ? Muttley@dastardlyhq.com - 2022-05-09 09:02 +0000
                Re: Anyone ever used vector<bool> ? Bo Persson <bo@bo-persson.se> - 2022-05-09 12:14 +0200
                Re: Anyone ever used vector<bool> ? Muttley@dastardlyhq.com - 2022-05-09 15:36 +0000
                Re: Anyone ever used vector<bool> ? James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-05-09 11:56 -0400
                Re: Anyone ever used vector<bool> ? Muttley@dastardlyhq.com - 2022-05-09 16:18 +0000
                Re: Anyone ever used vector<bool> ? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-05-09 09:38 -0700
                Re: Anyone ever used vector<bool> ? Muttley@dastardlyhq.com - 2022-05-10 15:55 +0000
                Re: Anyone ever used vector<bool> ? James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-05-10 13:28 -0400
                Re: Anyone ever used vector<bool> ? James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-05-10 10:16 -0400
                Re: Anyone ever used vector<bool> ? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-05-10 18:40 +0200
                Re: Anyone ever used vector<bool> ? Manfred <noname@add.invalid> - 2022-05-10 19:50 +0200
                Re: Anyone ever used vector<bool> ? Öö Tiib <ootiib@hot.ee> - 2022-05-12 05:44 -0700
                Re: Anyone ever used vector<bool> ? Manfred <noname@add.invalid> - 2022-05-12 17:24 +0200
                Re: Anyone ever used vector<bool> ? Öö Tiib <ootiib@hot.ee> - 2022-05-12 20:11 -0700
                Re: Anyone ever used vector<bool> ? James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-05-12 12:53 -0400
                Re: Anyone ever used vector<bool> ? James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-05-12 22:53 -0400
                Re: Anyone ever used vector<bool> ? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-05-13 18:34 +0200
                Re: Anyone ever used vector<bool> ? James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-05-13 23:46 -0400
                Re: Anyone ever used vector<bool> ? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-05-14 11:43 +0200
                Re: Anyone ever used vector<bool> ? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-05-15 07:48 -0700
                Re: Anyone ever used vector<bool> ? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-05-16 03:30 +0200
                Re: Anyone ever used vector<bool> ? James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-05-15 22:57 -0400
                Re: Anyone ever used vector<bool> ? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-05-17 05:30 -0700
                Re: Anyone ever used vector<bool> ? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-05-17 05:19 -0700
                Re: Anyone ever used vector<bool> ? Juha Nieminen <nospam@thanks.invalid> - 2022-05-16 05:46 +0000
                Re: Anyone ever used vector<bool> ? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-05-17 05:37 -0700
                Re: Anyone ever used vector<bool> ? wij <wyniijj2@gmail.com> - 2022-05-12 08:05 -0700
                Re: Anyone ever used vector<bool> ? scott@slp53.sl.home (Scott Lurndal) - 2022-05-09 17:20 +0000
                Re: Anyone ever used vector<bool> ? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-05-09 12:05 -0700
                Re: Anyone ever used vector<bool> ? Bo Persson <bo@bo-persson.se> - 2022-05-09 21:57 +0200
                Re: Anyone ever used vector<bool> ? wij <wyniijj2@gmail.com> - 2022-05-09 13:56 -0700
                Re: Anyone ever used vector<bool> ? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-05-09 08:33 -0700
                Re: Anyone ever used vector<bool> ? James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-05-09 11:56 -0400
                Re: Anyone ever used vector<bool> ? Manfred <noname@add.invalid> - 2022-05-09 18:13 +0200
                Re: Anyone ever used vector<bool> ? James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-05-10 10:14 -0400
                Re: Anyone ever used vector<bool> ? scott@slp53.sl.home (Scott Lurndal) - 2022-05-10 14:31 +0000
                Re: Anyone ever used vector<bool> ? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-05-07 18:38 +0200
                Re: Anyone ever used vector<bool> ? James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-05-07 18:28 -0400
                Re: Anyone ever used vector<bool> ? Manfred <noname@add.invalid> - 2022-05-08 18:37 +0200
                Re: Anyone ever used vector<bool> ? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-05-08 11:50 -0700
                Re: Anyone ever used vector<bool> ? James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-05-08 18:18 -0400
                Re: Anyone ever used vector<bool> ? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-05-07 09:45 -0700
                Re: Anyone ever used vector<bool> ? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-05-07 19:12 +0200
                Re: Anyone ever used vector<bool> ? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-05-07 20:36 -0700
                Re: Anyone ever used vector<bool> ? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-05-08 08:26 +0200
                Re: Anyone ever used vector<bool> ? scott@slp53.sl.home (Scott Lurndal) - 2022-05-06 13:55 +0000
                Re: Anyone ever used vector<bool> ? Juha Nieminen <nospam@thanks.invalid> - 2022-05-06 06:35 +0000
                Re: Anyone ever used vector<bool> ? Ben <ben.usenet@bsb.me.uk> - 2022-05-06 11:29 +0100
                Re: Anyone ever used vector<bool> ? Juha Nieminen <nospam@thanks.invalid> - 2022-05-09 04:58 +0000
                Re: Anyone ever used vector<bool> ? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-05-08 22:30 -0700
  Re: Anyone ever used vector<bool> ? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-05-03 14:41 -0700
  Re: Anyone ever used vector<bool> ? Andrea Venturoli <ml.diespammer@netfence.it> - 2022-05-04 08:20 +0200
  Re: Anyone ever used vector<bool> ? wij wij <wyniijj2@gmail.com> - 2022-05-04 03:21 -0700
    Re: Anyone ever used vector<bool> ? Muttley@dastardlyhq.com - 2022-05-04 10:52 +0000
  Re: Anyone ever used vector<bool> ? Juha Nieminen <nospam@thanks.invalid> - 2022-05-04 10:47 +0000
    Re: Anyone ever used vector<bool> ? Muttley@dastardlyhq.com - 2022-05-04 10:53 +0000
  Re: Anyone ever used vector<bool> ? Bonita Montero <Bonita.Montero@gmail.com> - 2022-06-01 05:46 +0200
    Re: Anyone ever used vector<bool> ? Bonita Montero <Bonita.Montero@gmail.com> - 2022-06-01 07:31 +0200
    Re: Anyone ever used vector<bool> ? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-06-01 14:20 +0200
      Re: Anyone ever used vector<bool> ? Bonita Montero <Bonita.Montero@gmail.com> - 2022-06-01 14:23 +0200
        Re: Anyone ever used vector<bool> ? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-06-01 14:26 +0200
          Re: Anyone ever used vector<bool> ? Bonita Montero <Bonita.Montero@gmail.com> - 2022-06-01 14:40 +0200

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