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From: David Kastrup <dak@gnu.org>
To: Walter Bright <boost@digitalmars.com>
Cc: git@vger.kernel.org
Subject: Re: [RFC] Convert builin-mailinfo.c to use The Better String   Library.
Date: Fri, 07 Sep 2007 10:26:08 +0200	[thread overview]
Message-ID: <851wda7ufz.fsf@lola.goethe.zz> (raw)
In-Reply-To: <fbr1a2$qm7$1@sea.gmane.org> (Walter Bright's message of "Fri\, 07 Sep 2007 01\:15\:06 -0700")

Walter Bright <boost@digitalmars.com> writes:

> A canonical example is that of a loop. Consider a simple C loop over
> an array:
>
> void foo(int array[10])
> {
>     for (int i = 0; i < 10; i++)
>     {   int value = array[i];
>         ... do something ...
>     }
> }
>
> It's simple, but it has a lot of problems:
>
> 1) i should be size_t, not int

Wrong.  size_t is for holding the size of memory objects in bytes, not
in terms of indices.  For indices, the best variable is of the same
type as the declared index maximum size, so here it is typeof(10),
namely int.

> 2) array is not checked for overflow

Why should it?

> 3) 10 may not be the actual array dimension

Your point is?

> 4) may be more efficient to step through the array with pointers,
> rather than indices

No.  It is a beginners' and advanced users' mistake to think using
pointers for access is a good idea.  Trivial optimizations are what a
compiler is best at, not the user.  Using pointer manipulation will
more often than not break loop unrolling, loop reversal, strength
reduction and other things.

> 5) type of array may change, but the type of value may not get
> updated

Huh?

> 6) crashes if array is NULL

Certainly.  Your point being?

> 7) only works with arrays and pointers

Since there are only arrays and pointers in C, not really a restriction.

>
> Since this thread is talking about C++, let's look at the C++ version:
>
> void foo(std::vector<int> array)
> {
>   for (std::vector<int>::const_iterator
>        i = array.begin();
>        i != array.end();
>        i++)
>   {
>     int value = *i;
>     ... do something ...
>   }
> }

Where is my barf bag?

> Frankly, I don't want to write loops that way. I want to write them
> like this:
>
> void foo(int[] array)
> {
>   foreach (value; array)
>   {
>     ... do something ...
>   }
> }
>
> As a programmer, I'm specifying exactly what I want to happen without
> much extra puffery. It's less typing, simpler, and more resistant to
> bugs.
>
> 1) correct loop index type is selected based on the type of array
> 2) arrays carry with them their dimension, so foreach is guaranteed to
> step through the loop the correct number of times
> 3) implementation decides if pointers will do a better job than
> indices, based on the compilation target
> 4) type of value is inferred automatically from the type of array, so
> no worries if the type changes
> 5) Null arrays have 0 length, so no crashing
> 6) works with any collection type

Most of those are toy concerns.  They prevent problems that don't
actually occur much in practice.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum

  reply	other threads:[~2007-09-07  8:26 UTC|newest]

Thread overview: 102+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-09-04 20:50 Lukas Sandström
2007-09-04 21:38 ` Alex Riesen
2007-09-04 23:01   ` Pierre Habouzit
2007-09-05 14:54 ` Kristian Høgsberg
2007-09-05 17:29   ` Matthieu Moy
2007-09-06  2:30     ` Miles Bader
2007-09-06  4:48     ` Dmitry Kakurin
2007-09-06  4:59       ` Shawn O. Pearce
2007-09-06  9:12         ` Andreas Ericsson
2007-09-06  9:35           ` Junio C Hamano
2007-09-06 10:21             ` Andreas Ericsson
2007-09-06  9:52           ` David Kastrup
2007-09-06  5:03       ` Miles Bader
2007-09-06 12:08         ` Johannes Schindelin
2007-09-06 17:50       ` Linus Torvalds
2007-09-07  0:21         ` Dmitry Kakurin
2007-09-07  0:38           ` Linus Torvalds
2007-09-07  1:08             ` Dmitry Kakurin
2007-09-07  1:27               ` Linus Torvalds
2007-09-07  3:09                 ` Dmitry Kakurin
2007-09-07  5:48                   ` David Symonds
2007-09-07  6:15                   ` Theodore Tso
2007-09-20 14:06                     ` Steven Burns
2007-09-20 14:56                       ` Andreas Ericsson
2007-09-07  6:31                   ` Andreas Ericsson
2007-09-07 22:17                     ` Dmitry Kakurin
2007-09-07 22:28                       ` David Kastrup
2007-09-08  0:37                         ` Dmitry Kakurin
2007-09-08  6:25                           ` David Kastrup
2007-09-09  0:29                       ` Andreas Ericsson
2007-09-07  6:52                   ` David Kastrup
2007-09-07 10:28                   ` Johannes Schindelin
2007-09-07 10:26                 ` Johannes Schindelin
2007-09-07  6:50               ` David Kastrup
2007-09-07  1:12             ` Linus Torvalds
2007-09-07  1:40               ` alan
2007-09-07  5:09               ` Walter Bright
2007-09-07  7:40                 ` David Kastrup
2007-09-07  8:15                   ` Walter Bright
2007-09-07  8:26                     ` David Kastrup [this message]
2007-09-07  9:14                       ` Walter Bright
2007-09-07  9:31                         ` David Kastrup
2007-09-07 20:22                           ` Walter Bright
2007-09-07 20:27                             ` David Kastrup
2007-09-07 23:16                               ` Walter Bright
2007-09-08 23:50                             ` Andreas Ericsson
2007-09-09  0:37                               ` Pierre Habouzit
2007-09-09  1:36                                 ` Andreas Ericsson
2007-09-07 11:36                   ` Wincent Colaiuta
2007-09-07  9:41                 ` Pierre Habouzit
2007-09-07 19:03                   ` Walter Bright
2007-09-07 19:31                     ` David Kastrup
2007-09-07 20:49                       ` Walter Bright
2007-09-07 19:41                     ` Pierre Habouzit
2007-09-07 19:51                       ` David Kastrup
2007-09-07 19:59                         ` Pierre Habouzit
2007-09-07 20:40                       ` Walter Bright
2007-09-07 20:56                         ` Pierre Habouzit
2007-09-07 22:54                           ` Walter Bright
2007-09-08  0:56               ` John 'Z-Bo' Zabroski
2007-09-08  6:36                 ` David Kastrup
2007-09-19 19:56               ` Steven Burns
2007-09-07  3:06           ` Wincent Colaiuta
2007-09-07  4:06             ` Paul Wankadia
2007-09-07  4:30               ` Nicolas Pitre
2007-09-07  9:19               ` Wincent Colaiuta
2007-09-07  6:25             ` Andreas Ericsson
2007-09-07 10:56               ` Johannes Schindelin
2007-09-07 11:54                 ` Andreas Ericsson
2007-09-07 12:33                   ` Wincent Colaiuta
2007-09-07 12:55                     ` Karl Hasselström
2007-09-07 13:58                     ` Andreas Ericsson
2007-09-07 14:13                       ` Wincent Colaiuta
2007-09-09  0:09                         ` Andreas Ericsson
2007-09-07 16:09                 ` David Kastrup
2007-09-07 11:30               ` Wincent Colaiuta
2007-09-07  8:36             ` Walter Bright
2007-09-07  9:41               ` Andreas Ericsson
2007-09-07 19:23                 ` Walter Bright
2007-09-07 19:40                   ` David Kastrup
2007-09-09  0:25                   ` Andreas Ericsson
2009-09-17 16:23                   ` Bernd Jendrissek
2007-09-07 11:52               ` Wincent Colaiuta
2007-09-07 19:25                 ` Walter Bright
2007-09-22 16:52               ` Steven Burns
2007-09-07  6:47           ` David Kastrup
2007-09-07  7:41             ` Andy Parkins
2007-09-07  8:08               ` David Kastrup
2007-09-07 10:21           ` Johannes Schindelin
2007-09-08  0:32             ` Dmitry Kakurin
2007-09-08  6:24               ` David Kastrup
2007-09-08 23:25               ` Alex Riesen
2007-09-24 13:41         ` figo
2007-09-24 13:57           ` David Kastrup
2007-09-25 19:19             ` Steven Burns
2007-09-25 19:55               ` David Kastrup
2012-05-22 18:30         ` Syed M Raihan
2010-06-10 19:12       ` Ian Molton
2010-06-11 12:23         ` Jakub Narebski
2010-06-11 13:33           ` Dario Rodriguez
2007-09-05 15:27 ` Kristian Høgsberg
2007-09-07 10:47 ` Lukas Sandström

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