Re: Concrete classes considered harmful

From	"Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com>
Newsgroups	comp.lang.c++
Subject	Re: Concrete classes considered harmful
Date	2015-07-11 06:07 +0200
Organization	A noiseless patient Spider
Message-ID	<mnq4mt$k83$1@dont-email.me> (permalink)
References	<y42dnfPZC9VKGj3InZ2dnUU78Q-dnZ2d@giganews.com> <DI-20150711052526@ram.dialup.fu-berlin.de>

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On 11-Jul-15 5:25 AM, Stefan Ram wrote:
> Mr Flibble <flibble@i42.co.uk> writes:
>> Dependencies on concrete classes are considered harmful and should be
>> replaced with dependencies on abstractions.
>
>    In C++, the term »concrete class« already has a different
>    meaning than assumed above. At least according to Bjarne
>    Stroustrup who explained:
>
>        »The basic idea of concrete classes is that (...) In
>        many important cases, such as a vector, that representation
>        is only one or more pointers to more data stored elsewhere,
>        but it is present in each object of a concrete class.«
>
>    So, if I understand Bjarne Stroustrup right, ::std::vector is /not/
>    a concrete class, because its representation is stored outside of
>    its instances. But according to your terminology, it would be a
>    »concrete class«, because it implements all it's member functions.

On the contrary, Bjarne uses std::vector as an example of a concrete class.

Quoting the relevant passage, indirectly from <url: 
http://programmers.stackexchange.com/questions/221437/concrete-types-as-described-by-stroustrup-c-programming-language-4th-ed>:

> The basic idea of concrete classes is that they behave “just like built-in
> types.” For example, a complex number type and an infinite-precision integer are
> much like built-in int, except of course that they have their own semantics and
> sets of operations. Similarly, a vector and a string are much like built-in
> arrays, except that they are better behaved (§ 4.2, § 4.3.2, § 4.4.1).
>
> The defining characteristic of a concrete type is that its representation is
> part of its definition. In many important cases, such as a vector, that
> representation is only one or more pointers to more data stored elsewhere, but
> it is present in each object of a concrete class.... In particular, it allows us
> to
>
> • place objects of concrete types on the stack, in statically allocated memory,
>   and in other objects (§ 6.4.2);
>
> • refer to objects directly (and not just through pointers or references);
>
> • initialize objects immediately and completely (e.g., using constructors;
>   § 2.3.2); and
>
> • copy objects (§ 3.3).
>
> Stroustrup, Bjarne (2013-07-10). The C++ Programming Language (4th Edition)
> (Section 16.3 Concrete Classes; Kindle Locations 2373-2386). Pearson Education.
> Kindle Edition.

Note: I find the discussion over on SO perplexing. But then much is 
perplexing there. It's the #1 Herb Schildt area of the net, AFAIK.

Cheers & hth.,

- Alf

-- 
Using Thunderbird as Usenet client, Eternal September as NNTP server.

Thread

Concrete classes considered harmful Mr Flibble <flibble@i42.co.uk> - 2015-07-11 04:04 +0100
  Re: Concrete classes considered harmful Ian Collins <ian-news@hotmail.com> - 2015-07-11 15:09 +1200
    Re: Concrete classes considered harmful Mr Flibble <flibble@i42.co.uk> - 2015-07-11 17:49 +0100
      Re: Concrete classes considered harmful Mr Flibble <flibble@i42.co.uk> - 2015-07-11 18:10 +0100
        Re: Concrete classes considered harmful Martin Shobe <martin.shobe@yahoo.com> - 2015-07-11 13:33 -0500
      Re: Concrete classes considered harmful Ian Collins <ian-news@hotmail.com> - 2015-07-12 09:17 +1200
        Re: Concrete classes considered harmful Mr Flibble <flibble@i42.co.uk> - 2015-07-12 01:51 +0100
          Re: Concrete classes considered harmful Ian Collins <ian-news@hotmail.com> - 2015-07-12 13:20 +1200
            Re: Concrete classes considered harmful Mr Flibble <flibble@i42.co.uk> - 2015-07-12 02:32 +0100
              Re: Concrete classes considered harmful Ian Collins <ian-news@hotmail.com> - 2015-07-12 15:48 +1200
                Re: Concrete classes considered harmful Mr Flibble <flibble@i42.co.uk> - 2015-07-12 13:46 +0100
              Re: Concrete classes considered harmful Ian Collins <ian-news@hotmail.com> - 2015-07-12 16:14 +1200
                Re: Concrete classes considered harmful legalize+jeeves@mail.xmission.com (Richard) - 2015-07-13 17:46 +0000
                Re: Concrete classes considered harmful Ian Collins <ian-news@hotmail.com> - 2015-07-14 08:52 +1200
                Re: Concrete classes considered harmful legalize+jeeves@mail.xmission.com (Richard) - 2015-07-13 22:01 +0000
            Re: Concrete classes considered harmful legalize+jeeves@mail.xmission.com (Richard) - 2015-07-13 17:28 +0000
              Re: Concrete classes considered harmful Ian Collins <ian-news@hotmail.com> - 2015-07-14 08:47 +1200
                Re: Concrete classes considered harmful legalize+jeeves@mail.xmission.com (Richard) - 2015-07-13 22:02 +0000
                Re: Concrete classes considered harmful Ian Collins <ian-news@hotmail.com> - 2015-07-14 10:35 +1200
                Re: Concrete classes considered harmful legalize+jeeves@mail.xmission.com (Richard) - 2015-07-14 04:52 +0000
                Re: Concrete classes considered harmful Ian Collins <ian-news@hotmail.com> - 2015-07-14 19:31 +1200
                Re: Concrete classes considered harmful legalize+jeeves@mail.xmission.com (Richard) - 2015-07-15 16:57 +0000
                Re: Concrete classes considered harmful Ian Collins <ian-news@hotmail.com> - 2015-07-16 09:49 +1200
                Re: Concrete classes considered harmful legalize+jeeves@mail.xmission.com (Richard) - 2015-07-16 15:53 +0000
                Re: Concrete classes considered harmful Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-10-08 13:20 +0000
                Re: Concrete classes considered harmful legalize+jeeves@mail.xmission.com (Richard) - 2015-10-12 20:48 +0000
      Re: Concrete classes considered harmful Juha Nieminen <nospam@thanks.invalid> - 2015-07-12 11:32 +0000
        Re: Concrete classes considered harmful Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2015-07-12 13:46 +0100
          Re: Concrete classes considered harmful Mr Flibble <flibble@i42.co.uk> - 2015-07-12 13:54 +0100
            Re: Concrete classes considered harmful Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2015-07-12 14:21 +0100
              Re: Concrete classes considered harmful Mr Flibble <flibble@i42.co.uk> - 2015-07-12 14:40 +0100
                Re: Concrete classes considered harmful Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2015-07-12 14:59 +0100
    Re: Concrete classes considered harmful legalize+jeeves@mail.xmission.com (Richard) - 2015-07-13 17:08 +0000
      Re: Concrete classes considered harmful Mr Flibble <flibble@i42.co.uk> - 2015-07-13 19:59 +0100
      Re: Concrete classes considered harmful Mr Flibble <flibble@i42.co.uk> - 2015-07-13 20:06 +0100
  Re: Concrete classes considered harmful "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2015-07-11 05:11 +0200
    Re: Concrete classes considered harmful legalize+jeeves@mail.xmission.com (Richard) - 2015-07-13 17:10 +0000
  Re: Concrete classes considered harmful "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2015-07-11 06:07 +0200
    Re: Concrete classes considered harmful woodbrian77@gmail.com - 2015-07-11 14:12 -0700
  Re: Concrete classes considered harmful Paavo Helde <myfirstname@osa.pri.ee> - 2015-07-11 02:06 -0500
    Re: Concrete classes considered harmful JiiPee <no@notvalid.com> - 2015-07-11 08:28 +0100
    Re: Concrete classes considered harmful Reinhardt Behm <rbehm@hushmail.com> - 2015-07-11 15:48 +0800
  Re: Concrete classes considered harmful Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2015-07-12 00:16 +0100
    Re: Concrete classes considered harmful Mr Flibble <flibble@i42.co.uk> - 2015-07-12 01:52 +0100
  Re: Concrete classes considered harmful David Harmon <source@netcom.com> - 2015-07-12 06:58 -0700
    Re: Concrete classes considered harmful Mr Flibble <flibble@i42.co.uk> - 2015-07-12 15:45 +0100
  Re: Concrete classes considered harmful Mr Flibble <flibble@i42.co.uk> - 2015-07-12 16:30 +0100
    Re: Concrete classes considered harmful woodbrian77@gmail.com - 2015-07-12 11:23 -0700
      Re: Concrete classes considered harmful "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2015-07-12 21:37 +0200
        Re: Concrete classes considered harmful woodbrian77@gmail.com - 2015-07-12 14:34 -0700
      Re: Concrete classes considered harmful Luca Risolia <luca.risolia@linux-projects.org> - 2015-07-13 00:38 +0200

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