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From: Derek Fawcus <dfawcus+lists-tuhs@employees.org>
To: tuhs@tuhs.org
Subject: Re: [TUHS] v7 K&R C
Date: Sun, 17 May 2020 17:34:37 +0100	[thread overview]
Message-ID: <20200517163437.GB5127@clarinet.employees.org> (raw)
In-Reply-To: <20200514172107.GI20771@mcvoy.com>

On Thu, May 14, 2020 at 10:21:07AM -0700, Larry McVoy wrote:
> On Wed, May 13, 2020 at 08:42:55PM -0400, John P. Linderman wrote:
> > I never liked call by reference. When I was trying to understand a chunk of
> > code, it was a great mental simplification to know that whatever a called
> > routine did, it couldn't have an effect on the code I was trying to
> > understand except through a returned value and (ghastly) global variables.

That has always been my issue with the C++ references, that one could not
read a piece of code in isolation, and know when a reference may be made.

I guess I'd be happy with references if the syntax always required one to
write '&x' when they're being created, then the called function can choose
if it either wishes to use a pointer or a reference, the only difference
being the syntax used to deref the reference.

As to Doug's point about new arithmetic types and overloading, I recall
a few years ago reading on the 9fans list about an extension there (in KenC?)
which supported them in C.  I've not managed to dig up the details again,
maybe someone else could.  As I recall it involved defining structs.

> Call by value is fine for things like a single integer or whatever.  When
> you have some giant array, you want to pass a pointer.
> 
> And "const" helps a lot with indicating the subroutine isn't going to
> change it.

However that is simply the ABI, i.e. it should be possible for a sufficiently
clever compiler to implement such a call-by-value as a call-by-constish-reference.

i.e. this:
    somefn(struct s p) {...}
    struct s ss;  somefn(ss);

in effect becomes syntax sugar for:
    somefn(constish ref struct s p) {...}
    struct s ss;  somefn(&ss);

Where 'constish' does not allow 'ss' to be altered even if somefn() assigns
to 'p', because in that case it would do sufficient copying so as to
make things work.  There was a proposed MIPS ABI which stated this.

The current C semantics in effect do that, but with the ABIs always having
the caller make a copy and pass a reference to it, rather than allowing the
callee to make a copy if/when required.

DF

  reply	other threads:[~2020-05-17 16:34 UTC|newest]

Thread overview: 153+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-25  1:59 Adam Thornton
2020-04-25  2:37 ` Charles Anthony
2020-04-25  2:47   ` Adam Thornton
2020-04-25  2:51     ` Rob Pike
2020-04-25  2:54       ` Rob Pike
2020-04-25  3:04         ` Larry McVoy
2020-04-25  3:30           ` Clem Cole
2020-04-25  3:43             ` Larry McVoy
2020-04-25  3:54               ` Jon Steinhart
2020-04-25 11:44                 ` Michael Kjörling
2020-04-25 13:17             ` Dan Cross
2020-05-11  0:28         ` scj
2020-05-11  0:32           ` Rob Pike
2020-05-11  0:57             ` Larry McVoy
2020-05-11 17:32               ` Greg A. Woods
2020-05-11 18:25                 ` Paul Winalski
2020-05-11 18:37                   ` Clem Cole
2020-05-11 19:12                     ` Paul Winalski
2020-05-11 19:57                       ` joe mcguckin
2020-05-11 20:25                         ` Larry McVoy
2020-05-12 17:23                           ` Paul Winalski
2020-05-12 17:35                             ` ron
2020-05-12 17:42                               ` Larry McVoy
2020-05-12 18:36                               ` Paul Winalski
2020-05-13 23:36                             ` Dave Horsfall
2020-05-14  0:42                               ` John P. Linderman
2020-05-14  2:44                                 ` Rich Morin
2020-05-14  3:09                                   ` Charles Anthony
2020-05-14 12:27                                     ` ron
2020-05-14 12:27                                     ` ron
2020-05-14 12:27                                     ` ron
2020-05-14  7:38                                   ` Dave Horsfall
2020-05-14 12:25                                     ` ron
2020-05-14 17:13                                   ` Paul Winalski
2020-05-14 17:21                                 ` Larry McVoy
2020-05-17 16:34                                   ` Derek Fawcus [this message]
2020-05-14  4:21                               ` Greg A. Woods
2020-05-14  4:40                                 ` Warner Losh
2020-05-14 17:32                               ` Larry McVoy
2020-05-14 22:32                                 ` Tony Finch
2020-05-16 23:53                                   ` Steffen Nurpmeso
2020-05-16 23:59                                     ` [TUHS] v7 K&R C [really lexers] Jon Steinhart
2020-05-17  0:04                                       ` Brantley Coile
2020-05-17  1:23                                         ` Warner Losh
2020-05-17  1:36                                           ` Brantley Coile
2020-06-13 21:24                                           ` scj
2020-06-14  8:47                                             ` arnold
2020-06-14 12:52                                             ` Richard Salz
2020-06-14 14:03                                               ` Ralph Corderoy
2020-06-14 14:26                                                 ` arnold
2020-06-14 14:48                                                   ` Ralph Corderoy
2020-06-15  1:12                                                     ` Warren Toomey
2020-06-15  1:29                                                       ` Warren Toomey
2020-06-15  6:06                                                         ` arnold
2020-05-17 16:31                                       ` Paul Winalski
2020-05-17  0:35                                     ` [TUHS] v7 K&R C Larry McVoy
2020-05-11 18:37                   ` Larry McVoy
2020-05-11  2:08           ` Lawrence Stewart
2020-05-11 11:36           ` Michael Kjörling
2020-04-25  3:37       ` Dave Horsfall
2020-04-27 13:19       ` Tony Finch
2020-04-25  2:50   ` Adam Thornton
2020-04-25  5:59     ` Lars Brinkhoff
2020-04-25 13:11 Noel Chiappa
2020-04-25 13:18 ` Rob Pike
2020-04-25 14:57   ` Warner Losh
2020-04-25 18:03   ` Noel Chiappa
2020-04-25 20:11     ` Michael Kjörling
2020-04-25 21:27       ` Brian L. Stuart
2020-04-26  0:07     ` emanuel stiebler
2020-04-26  0:54     ` Rob Pike
2020-04-26 19:37     ` Derek Fawcus
2020-04-26 20:10       ` Derek Fawcus
2020-04-26 21:59         ` Rich Morin
2020-04-26 22:38         ` Noel Hunt
2020-04-26 23:57         ` Nemo Nusquam
2020-04-27  3:38           ` Rob Pike
2020-04-25 13:35 ` Hellwig Geisse
2020-04-25 13:59   ` Richard Salz
2020-04-25 19:01   ` Brian L. Stuart
2020-04-25 20:07     ` Michael Kjörling
2020-04-25 21:34       ` Brian L. Stuart
2020-04-26  6:40     ` arnold
2020-04-25 19:41 Noel Chiappa
2020-04-25 20:27 ` Steffen Nurpmeso
2020-04-27 17:45 Noel Chiappa
2020-04-27 17:56 ` Richard Salz
2020-04-27 18:02 ` Brantley Coile
2020-04-27 18:47 ` Derek Fawcus
     [not found] <mailman.1.1589421601.13778.tuhs@minnie.tuhs.org>
2020-05-14  3:02 ` Paul McJones
2020-05-14 17:08   ` Paul Winalski
2020-05-14 17:58     ` Clem Cole
2020-05-14 18:41 Doug McIlroy
2020-05-14 18:45 ` Richard Salz
2020-05-14 20:54 ` Clem Cole
2020-05-15  2:44 ` Rob Pike
2020-05-15  3:57   ` Rich Morin
2020-05-15  7:55   ` Dr Iain Maoileoin
2020-05-15 15:01     ` Larry McVoy
2020-05-15 15:36       ` John P. Linderman
2020-05-15 20:01         ` ron
2020-05-15 20:03           ` Larry McVoy
2020-05-15 20:05           ` Clem Cole
2020-05-15 20:18             ` ron
2020-05-15 20:24               ` Clem Cole
2020-05-16  0:57               ` Brantley Coile
2020-05-16 16:14                 ` Dan Cross
2020-05-15 20:56           ` Steve Nickolas
2020-05-16  0:31             ` Peter Jeremy
2020-05-16  8:30               ` Steve Nickolas
2020-05-16  0:43           ` John P. Linderman
2020-05-16 16:28             ` Paul Winalski
2020-05-16 17:39               ` Warner Losh
2020-05-19 19:45                 ` Peter Pentchev
2020-05-20  3:52                   ` Rich Morin
2020-05-21 15:06                     ` Dave Horsfall
2020-05-15 20:34 Doug McIlroy
2020-05-15 20:40 ` Warner Losh
2020-05-15 21:31 Richard Tobin
2020-05-15 21:53 ` Steve Nickolas
2020-05-15 22:33   ` ron
2020-05-15 23:34     ` Steffen Nurpmeso
2020-05-16  1:26       ` Larry McVoy
2020-05-16 21:59       ` Ronald Natalie
2020-05-16 23:26         ` Steffen Nurpmeso
2020-05-17 16:24           ` Paul Winalski
2020-05-17 16:29             ` ron
2020-05-17 16:38               ` Paul Winalski
2020-05-17 20:08                 ` Clem Cole
2020-05-18  8:46                   ` Peter Jeremy
2020-05-19  7:41                     ` Dave Horsfall
2020-05-18 12:04             ` Tony Finch
2020-05-18 13:10               ` Clem Cole
2020-05-18 15:13             ` Rich Morin
2020-05-18 15:51               ` Brantley Coile
2020-05-18 16:11             ` Dan Cross
2020-05-18 21:18               ` ron
2020-05-17 16:10 ` Derek Fawcus
2020-05-17 16:14   ` ron
2020-05-16  0:15 Nelson H. F. Beebe
2020-05-16  0:28 ` Steffen Nurpmeso
2020-05-16  1:52 ` Warner Losh
2020-05-16 16:31   ` Paul Winalski
2020-05-16 20:35     ` Brad Spencer
2020-05-16 20:37       ` Warner Losh
2020-05-18 12:25     ` Tony Finch
2020-05-16 18:45 Richard Tobin
2020-05-16 21:55 ` Ronald Natalie
2020-05-18 13:58 Doug McIlroy
2020-05-18 14:33 Doug McIlroy
2020-05-19  2:29 Doug McIlroy
2020-05-19  3:20 ` Steve Nickolas
2020-05-19 12:29 Noel Chiappa

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