Re: On generally accepted terminology for pointers and arrays

From	"Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com>
Newsgroups	comp.lang.c++
Subject	Re: On generally accepted terminology for pointers and arrays
Date	2011-04-12 22:14 +0200
Organization	A noiseless patient Spider
Message-ID	<io2brp$nbc$1@dont-email.me> (permalink)
References	<io0bnr$dph$1@dont-email.me> <57d23fe9-b1e2-483c-a2da-f327d8025503@v10g2000yqn.googlegroups.com> <0188c859-2681-4fad-b2bb-1cab739bdbbb@i14g2000yqe.googlegroups.com>

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* gwowen, on 12.04.2011 09:16:
> On Apr 12, 7:24 am, gwowen<gwo...@gmail.com>  wrote:
>
> [replying to self - bad me]
>
>> Speaking personally, I find it helpful to think of pointers as
>> modelling two distinct concepts.
>>
>> i) A nullable, reseatable reference to a single (possibly polymorphic)
>> object.
>> I can use it to access the members of the base type to which it has
>> been declared to point.  Trying anything else is fraught with danger
>> (even obtaiining a copy of the object (due to slicing)).
>
> [
>   other safe things :-
>   downcasting to a pointer-to-type-from-which-our-pointed-to-type is
> derived.
>   upcasting to a pointer-to-more-derived-type, as long as I check for
> dynamic_cast<>  returning NULL
> ]
>
>
>> ii) A bi-directional iterator into a contiguous collection of non-
>> polymorphic objects.
>
> [
>   I meant "random access iterator" not bidirectional, with the array
> access ptr[n] being syntactic sugar for *(ptr+n)
> ]

The "points into" is quite useful, I think not technically (because technically 
any pointing into middle of array is also a pointing to start of sub-array, 
ouch!) but it allows people some terminological & psychological elbow-room. ;-)

   * * *

Re "downcast" and "upcast", you got those directions backward wrt. common 
terminology, but I think you were aware of that possibility since you took such 
pains to describe what you meant in detail.

With conventional terminology, for single inheritance "up" is in the direction 
up the class inheritance chain, towards the top base class, and "down" is in the 
direction down the chain, towards the most specific derived class.

In the more general case we have a class derivation tree with many roots, but 
the same applies: the roots are in the direction of up.

However, it has not always been a universal convention to think of and draw such 
abstract trees with root(s) upward. Donald Knuth changed his presentation from 
first edition to second edition of "The Art of Computer Programming". So, 
somewhere there at the start of the 1970's, apparently, the notion of trees with 
roots in the air, became the common way to think of it and talk about it.

   * * *

Re the two kinds of pointers, yes it's technically a shortcoming of the C++ type 
system. But then so is the failure to distinguish pointers to automatically 
allocated objects from pointers to dynamically allocated objects. And so on. The 
various combinations of properties to distinguish explodes exponentially. I'm 
not aware of any good answer, although a RAND corporation employee (as I recall) 
once posted to clc++m a proposal to replace use of raw pointers with use of 
smart pointers that modeled these concepts/distinctions.

Cheers & hth.,

- Alf

-- 
blog at <url: http://alfps.wordpress.com>

Thread

On generally accepted terminology for pointers and arrays "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-04-12 04:00 +0200
  Re: On generally accepted terminology for pointers and arrays Pavel <pauldontspamtolk@removeyourself.dontspam.yahoo> - 2011-04-12 00:13 -0400
  Re: On generally accepted terminology for pointers and arrays "Paul" <pchristor@yahoo.co.uk> - 2011-04-12 05:17 +0100
    Re: On generally accepted terminology for pointers and arrays Leigh Johnston <leigh@i42.co.uk> - 2011-04-12 14:02 +0100
      Re: On generally accepted terminology for pointers and arrays "Paul" <pchristor@yahoo.co.uk> - 2011-04-12 14:10 +0100
        Re: On generally accepted terminology for pointers and arrays Leigh Johnston <leigh@i42.co.uk> - 2011-04-12 14:49 +0100
      Re: On generally accepted terminology for pointers and arrays cg_chas <cg_chas@hotmail.com> - 2011-04-12 10:05 -0400
  Re: On generally accepted terminology for pointers and arrays cg_chas <cg_chas@hotmail.com> - 2011-04-12 01:11 -0400
  Re: On generally accepted terminology for pointers and arrays gwowen <gwowen@gmail.com> - 2011-04-11 23:24 -0700
    Re: On generally accepted terminology for pointers and arrays gwowen <gwowen@gmail.com> - 2011-04-12 00:16 -0700
      Re: On generally accepted terminology for pointers and arrays Leigh Johnston <leigh@i42.co.uk> - 2011-04-12 13:53 +0100
        Re: On generally accepted terminology for pointers and arrays "Paul" <pchristor@yahoo.co.uk> - 2011-04-12 14:08 +0100
      Re: On generally accepted terminology for pointers and arrays "Paul" <pchristor@yahoo.co.uk> - 2011-04-12 14:05 +0100
        Re: On generally accepted terminology for pointers and arrays Leigh Johnston <leigh@i42.co.uk> - 2011-04-12 14:48 +0100
          Re: On generally accepted terminology for pointers and arrays Ian Collins <ian-news@hotmail.com> - 2011-04-13 07:53 +1200
      Re: On generally accepted terminology for pointers and arrays "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-04-12 22:14 +0200
        Re: On generally accepted terminology for pointers and arrays Öö Tiib <ootiib@hot.ee> - 2011-04-12 15:39 -0700
    Re: On generally accepted terminology for pointers and arrays Goran <goran.pusic@gmail.com> - 2011-04-12 01:39 -0700
      Re: On generally accepted terminology for pointers and arrays Ian Collins <ian-news@hotmail.com> - 2011-04-12 20:51 +1200
    Re: On generally accepted terminology for pointers and arrays Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-04-12 21:51 +0000
  Re: On generally accepted terminology for pointers and arrays cpp4ever <n2xssvv.g02gfr12930@ntlworld.com> - 2011-04-12 09:59 +0100
    Re: On generally accepted terminology for pointers and arrays "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-04-12 16:25 +0200
      Re: On generally accepted terminology for pointers and arrays cpp4ever <n2xssvv.g02gfr12930@ntlworld.com> - 2011-04-12 16:07 +0100
        Re: On generally accepted terminology for pointers and arrays "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-04-12 17:32 +0200
          Re: On generally accepted terminology for pointers and arrays cpp4ever <n2xssvv.g02gfr12930@ntlworld.com> - 2011-04-12 16:53 +0100
            Re: On generally accepted terminology for pointers and arrays "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-04-12 18:16 +0200
              Re: On generally accepted terminology for pointers and arrays cpp4ever <n2xssvv.g02gfr12930@ntlworld.com> - 2011-04-12 17:39 +0100
                Re: On generally accepted terminology for pointers and arrays "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-04-12 19:32 +0200
                Re: DILLIGAF cpp4ever <n2xssvv.g02gfr12930@ntlworld.com> - 2011-04-12 19:05 +0100
                Re: DILLIGAF Peter Remmers <p.remmers@expires-2011-04-30.arcornews.de> - 2011-04-12 20:36 +0200
                Re: DILLIGAF cpp4ever <n2xssvv.g02gfr12930@ntlworld.com> - 2011-04-12 20:47 +0100
                Re: DILLIGAF gwowen <gwowen@gmail.com> - 2011-04-12 14:48 -0700
                Re: DILLIGAF Öö Tiib <ootiib@hot.ee> - 2011-04-12 15:16 -0700
    Re: On generally accepted terminology for pointers and arrays "Paul" <pchristor@yahoo.co.uk> - 2011-04-12 17:48 +0100
  Re: On generally accepted terminology for pointers and arrays Noah Roberts <dont@email.me> - 2011-04-12 09:37 -0700
    Re: On generally accepted terminology for pointers and arrays "Paul" <pchristor@yahoo.co.uk> - 2011-04-12 18:34 +0100
    Re: On generally accepted terminology for pointers and arrays "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-04-12 19:38 +0200
      Re: On generally accepted terminology for pointers and arrays Noah Roberts <dont@email.me> - 2011-04-12 11:00 -0700
        Re: On generally accepted terminology for pointers and arrays "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-04-12 20:03 +0200
          Re: On generally accepted terminology for pointers and arrays Noah Roberts <dont@email.me> - 2011-04-12 11:06 -0700
            Re: On generally accepted terminology for pointers and arrays Peter Remmers <p.remmers@expires-2011-04-30.arcornews.de> - 2011-04-12 20:26 +0200
              Re: On generally accepted terminology for pointers and arrays Noah Roberts <dont@email.me> - 2011-04-12 11:33 -0700
                Re: On generally accepted terminology for pointers and arrays Peter Remmers <p.remmers@expires-2011-04-30.arcornews.de> - 2011-04-12 20:55 +0200
                Re: On generally accepted terminology for pointers and arrays "Paul" <pchristor@yahoo.co.uk> - 2011-04-12 20:14 +0100
                Re: On generally accepted terminology for pointers and arrays Noah Roberts <dont@email.me> - 2011-04-12 12:47 -0700
                Re: On generally accepted terminology for pointers and arrays Peter Remmers <p.remmers@expires-2011-04-30.arcornews.de> - 2011-04-12 22:40 +0200
      Re: On generally accepted terminology for pointers and arrays cg_chas <cg_chas@hotmail.com> - 2011-04-12 14:15 -0400
        Re: On generally accepted terminology for pointers and arrays "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-04-12 20:52 +0200
          Re: On generally accepted terminology for pointers and arrays "Paul" <pchristor@yahoo.co.uk> - 2011-04-12 20:23 +0100
          Re: On generally accepted terminology for pointers and arrays cg_chas <cg_chas@hotmail.com> - 2011-04-12 16:01 -0400
            Re: On generally accepted terminology for pointers and arrays Noah Roberts <dont@email.me> - 2011-04-12 13:46 -0700
              Re: On generally accepted terminology for pointers and arrays Öö Tiib <ootiib@hot.ee> - 2011-04-12 19:49 -0700
                Re: On generally accepted terminology for pointers and arrays hanukas <jukka@liimatta.org> - 2011-04-13 00:06 -0700
                Re: On generally accepted terminology for pointers and arrays cg_chas <cg_chas@hotmail.com> - 2011-04-13 04:14 -0400
                Re: On generally accepted terminology for pointers and arrays Öö Tiib <ootiib@hot.ee> - 2011-04-13 07:53 -0700
                Re: On generally accepted terminology for pointers and arrays "Paul" <pchristor@yahoo.co.uk> - 2011-04-13 09:52 +0100
                Re: On generally accepted terminology for pointers and arrays cg_chas <cg_chas@hotmail.com> - 2011-04-13 05:20 -0400
                Re: On generally accepted terminology for pointers and arrays "Paul" <pchristor@yahoo.co.uk> - 2011-04-13 10:31 +0100
                Re: On generally accepted terminology for pointers and arrays cg_chas <cg_chas@hotmail.com> - 2011-04-13 07:04 -0400
                Re: On generally accepted terminology for pointers and arrays "Paul" <pchristor@yahoo.co.uk> - 2011-04-13 12:35 +0100
                Re: On generally accepted terminology for pointers and arrays cg_chas <cg_chas@hotmail.com> - 2011-04-13 07:41 -0400
                Re: On generally accepted terminology for pointers and arrays Ian Collins <ian-news@hotmail.com> - 2011-04-14 07:47 +1200
                Re: On generally accepted terminology for pointers and arrays "Paul" <pchristor@yahoo.co.uk> - 2011-04-14 11:44 +0100
                Re: On generally accepted terminology for pointers and arrays "io_x" <a@b.c.invalid> - 2011-04-13 18:41 +0200
                Re: On generally accepted terminology for pointers and arrays Noah Roberts <dont@email.me> - 2011-04-13 09:35 -0700
                Re: On generally accepted terminology for pointers and arrays "Paul" <pchristor@yahoo.co.uk> - 2011-04-13 20:17 +0100
              Re: On generally accepted terminology for pointers and arrays cg_chas <cg_chas@hotmail.com> - 2011-04-13 04:33 -0400
                Re: On generally accepted terminology for pointers and arrays cg_chas <cg_chas@hotmail.com> - 2011-04-13 04:35 -0400
            Re: On generally accepted terminology for pointers and arrays "Paul" <pchristor@yahoo.co.uk> - 2011-04-13 01:19 +0100
              Re: On generally accepted terminology for pointers and arrays cg_chas <cg_chas@hotmail.com> - 2011-04-13 04:01 -0400
                Re: On generally accepted terminology for pointers and arrays cg_chas <cg_chas@hotmail.com> - 2011-04-13 04:20 -0400
                Re: On generally accepted terminology for pointers and arrays "Paul" <pchristor@yahoo.co.uk> - 2011-04-13 09:56 +0100
                Re: On generally accepted terminology for pointers and arrays cg_chas <cg_chas@hotmail.com> - 2011-04-13 05:24 -0400
                Re: On generally accepted terminology for pointers and arrays "Paul" <pchristor@yahoo.co.uk> - 2011-04-13 10:34 +0100
                Re: On generally accepted terminology for pointers and arrays cg_chas <cg_chas@hotmail.com> - 2011-04-13 07:07 -0400
                Re: On generally accepted terminology for pointers and arrays "Paul" <pchristor@yahoo.co.uk> - 2011-04-13 12:36 +0100
                Re: On generally accepted terminology for pointers and arrays cg_chas <cg_chas@hotmail.com> - 2011-04-13 07:43 -0400
                Re: On generally accepted terminology for pointers and arrays "Paul" <pchristor@yahoo.co.uk> - 2011-04-13 13:18 +0100
                Re: On generally accepted terminology for pointers and arrays cg_chas <cg_chas@hotmail.com> - 2011-04-13 08:30 -0400
            Re: On generally accepted terminology for pointers and arrays "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-04-13 15:57 +0200
              Re: On generally accepted terminology for pointers and arrays Leigh Johnston <leigh@i42.co.uk> - 2011-04-13 15:10 +0100
              Re: On generally accepted terminology for pointers and arrays cg_chas <cg_chas@hotmail.com> - 2011-04-13 11:09 -0400
                Re: On generally accepted terminology for pointers and arrays cg_chas <cg_chas@hotmail.com> - 2011-04-13 12:04 -0400
            Re: On generally accepted terminology for pointers and arrays Noah Roberts <dont@email.me> - 2011-04-13 09:56 -0700
              Re: On generally accepted terminology for pointers and arrays cg_chas <cg_chas@hotmail.com> - 2011-04-13 14:11 -0400
      Re: On generally accepted terminology for pointers and arrays "Paul" <pchristor@yahoo.co.uk> - 2011-04-12 19:29 +0100
  Re: On generally accepted terminology for pointers and arrays Joshua Maurice <joshuamaurice@gmail.com> - 2011-04-12 09:36 -0700

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