Re: New directions in C: Default arguments

From	Bartc <bc@freeuk.com>
Newsgroups	comp.lang.c
Subject	Re: New directions in C: Default arguments
Date	2015-03-16 18:12 +0000
Organization	A noiseless patient Spider
Message-ID	<me76cp$b8d$1@dont-email.me> (permalink)
References	(8 earlier) <14f98f84-8033-4b26-ada1-305d89491e7e@googlegroups.com> <me51nf$2ha$1@dont-email.me> <87mw3d0xcl.fsf@kst-u.example.com> <me70mb$h53$1@dont-email.me> <_4ENw.20099$7U.13751@fx31.iad>

Show all headers | View raw

On 16/03/2015 17:07, Greg Martin wrote:
> On 2015-03-16, Martin Shobe <martin.shobe@yahoo.com> wrote:

>> For example (using . to identify keywords as seen else thread) the
>> following would all be compatible.
>>
>> void func(int w, int x, int .y, int .z);
>> void func(int x, int w, int .y, int .z);
>> void func(int, int, int .y, int .z);
>>
>> However, the following would not be compatible with the above and would
>> require a diagnostic if they both appeared in the same scope.
>>
>> void func(int w, int x, int .z, int .y);

>
> What would this buy you, over using a structure to pass the arguments?
> I'm not sure it would be worth the effort.
>
> A structure as an argument allows some defaulting of arguments as well
> as implicit named parameters. Admittedly the default arguments are
> limited.

You seriously think using a struct is nearly as good as using 
named/default arguments? OK, let's look at the disadvantages of using 
structs:

(1) You now have to create a corresponding struct for each of the 
hundreds of functions you might want to use named arguments for.

(2) You have to maintain a function parameter list *and* its struct.

(3) Each function, especially if applying this retroactively to an 
existing application, now has to be rewritten to use a single struct 
argument.

(4) Within each function, each a, b, c, d parameter now has to be 
written x.a, x.b, x.c, c.d etc.

(5) You have the extra overheads of passing a struct by value.

(6) In the caller, you either have to declare and initialise a struct 
separately, then pass it as fn(&s), which now becomes unreadable, or..

(7) ...use the ugly compound literal syntax (Martin gave an example of 
what that looks like.

(8) You can't now /optionally/ use either normal arguments to a 
function, or default/named parameters; it's all or nothing. Which means 
if introducing this to an existing application, you have to rewrite it.

(9) As you pointed out, you don't have much choice about default values 
(actually I'm not even sure that 0 is guaranteed with compound literals).

(10) In all, it will be such a painful, ungainly and unreadable way of 
doing it, that no-one will bother.

Of course using proper named/default arguments has its own disadvantage:

(1) You have to name the parameters in the function prototype, if one is 
used.

Once done however, you don't have to change anything else; you can 
optionally use the feature on a call-by-call basis. It is also easier to 
write, more readable, and requires little maintenance beyond what is 
needed anyway when a function interface changes.

-- 
Bartc

Thread

New directions in C: Default arguments jacob navia <jacob@spamsink.net> - 2015-03-14 23:11 +0100
  Re: New directions in C: Default arguments fir <profesor.fir@gmail.com> - 2015-03-14 18:17 -0700
    Re: New directions in C: Default arguments Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-03-15 11:25 +0000
      Re: New directions in C: Default arguments fir <profesor.fir@gmail.com> - 2015-03-15 07:18 -0700
        Re: New directions in C: Default arguments Bartc <bc@freeuk.com> - 2015-03-15 14:32 +0000
          Re: New directions in C: Default arguments fir <profesor.fir@gmail.com> - 2015-03-15 08:30 -0700
            Re: New directions in C: Default arguments fir <profesor.fir@gmail.com> - 2015-03-15 09:05 -0700
              Re: New directions in C: Default arguments fir <profesor.fir@gmail.com> - 2015-03-15 10:15 -0700
                Re: New directions in C: Default arguments fir <profesor.fir@gmail.com> - 2015-03-15 15:03 -0700
                Re: New directions in C: Default arguments Bartc <bc@freeuk.com> - 2015-03-15 22:40 +0000
                Re: New directions in C: Default arguments fir <profesor.fir@gmail.com> - 2015-03-15 16:04 -0700
                Re: New directions in C: Default arguments Keith Thompson <kst-u@mib.org> - 2015-03-16 08:35 -0700
                Re: New directions in C: Default arguments David Brown <david.brown@hesbynett.no> - 2015-03-16 16:45 +0100
                Re: New directions in C: Default arguments Keith Thompson <kst-u@mib.org> - 2015-03-16 11:36 -0700
                Re: New directions in C: Default arguments Philip Lantz <prl@canterey.us> - 2015-03-17 02:09 -0700
                Re: New directions in C: Default arguments Bartc <bc@freeuk.com> - 2015-03-17 12:44 +0000
                Re: New directions in C: Default arguments Philip Lantz <prl@canterey.us> - 2015-03-17 11:07 -0700
                Re: New directions in C: Default arguments Martin Shobe <martin.shobe@yahoo.com> - 2015-03-16 11:35 -0500
                Re: New directions in C: Default arguments Greg Martin <greg.at.softsprocket@dot.com> - 2015-03-16 17:07 +0000
                Re: New directions in C: Default arguments Martin Shobe <martin.shobe@yahoo.com> - 2015-03-16 12:40 -0500
                Re: New directions in C: Default arguments Bartc <bc@freeuk.com> - 2015-03-16 18:12 +0000
                Re: New directions in C: Default arguments Greg Martin <greg.at.softsprocket@dot.com> - 2015-03-16 18:30 +0000
                Re: New directions in C: Default arguments Martin Shobe <martin.shobe@yahoo.com> - 2015-03-16 13:52 -0500
                Re: New directions in C: Default arguments Greg Martin <greg.at.softsprocket@dot.com> - 2015-03-16 19:35 +0000
                Re: New directions in C: Default arguments Martin Shobe <martin.shobe@yahoo.com> - 2015-03-16 14:52 -0500
                Re: New directions in C: Default arguments Greg Martin <greg.at.softsprocket@dot.com> - 2015-03-16 20:27 +0000
                Re: New directions in C: Default arguments Bartc <bc@freeuk.com> - 2015-03-16 19:44 +0000
                Re: New directions in C: Default arguments Greg Martin <greg.at.softsprocket@dot.com> - 2015-03-16 19:55 +0000
                Re: New directions in C: Default arguments Bartc <bc@freeuk.com> - 2015-03-16 20:23 +0000
                Re: New directions in C: Default arguments Greg Martin <greg.at.softsprocket@dot.com> - 2015-03-16 20:53 +0000
                Re: New directions in C: Default arguments fir <profesor.fir@gmail.com> - 2015-03-16 14:33 -0700
                Re: New directions in C: Default arguments Keith Thompson <kst-u@mib.org> - 2015-03-16 11:44 -0700
                Re: New directions in C: Default arguments Martin Shobe <martin.shobe@yahoo.com> - 2015-03-16 13:59 -0500
  Re: New directions in C: Default arguments Bartc <bc@freeuk.com> - 2015-03-15 01:33 +0000
    Re: New directions in C: Default arguments fir <profesor.fir@gmail.com> - 2015-03-15 00:59 -0700
    Re: New directions in C: Default arguments David Brown <david.brown@hesbynett.no> - 2015-03-15 23:45 +0100
      Re: New directions in C: Default arguments fir <profesor.fir@gmail.com> - 2015-03-15 16:21 -0700
        Re: New directions in C: Default arguments David Brown <david.brown@hesbynett.no> - 2015-03-16 11:41 +0100
          Re: New directions in C: Default arguments Bartc <bc@freeuk.com> - 2015-03-16 11:13 +0000
            Re: New directions in C: Default arguments David Brown <david.brown@hesbynett.no> - 2015-03-16 13:19 +0100
              Re: New directions in C: Default arguments Bartc <bc@freeuk.com> - 2015-03-16 12:38 +0000
                Re: New directions in C: Default arguments David Brown <david.brown@hesbynett.no> - 2015-03-16 13:51 +0100
                Re: New directions in C: Default arguments Bartc <bc@freeuk.com> - 2015-03-16 13:21 +0000
                Re: New directions in C: Default arguments David Brown <david.brown@hesbynett.no> - 2015-03-16 15:12 +0100
                Re: New directions in C: Default arguments Richard Heathfield <rjh@cpax.org.uk> - 2015-03-16 14:24 +0000
                Re: New directions in C: Default arguments David Brown <david.brown@hesbynett.no> - 2015-03-16 16:09 +0100
                Re: New directions in C: Default arguments Richard Heathfield <rjh@cpax.org.uk> - 2015-03-16 18:11 +0000
                Re: New directions in C: Default arguments David Brown <david.brown@hesbynett.no> - 2015-03-17 13:23 +0100
                Re: New directions in C: Default arguments Richard Heathfield <rjh@cpax.org.uk> - 2015-03-17 12:28 +0000
                Re: New directions in C: Default arguments jacob navia <jacob@spamsink.net> - 2015-03-17 13:33 +0100
                Re: New directions in C: Default arguments fir <profesor.fir@gmail.com> - 2015-03-17 08:20 -0700
                Re: New directions in C: Default arguments fir <profesor.fir@gmail.com> - 2015-03-17 15:16 -0700
      Re: New directions in C: Default arguments jacob navia <jacob@spamsink.net> - 2015-03-16 11:38 +0100
        Re: New directions in C: Default arguments Bartc <bc@freeuk.com> - 2015-03-16 10:51 +0000
          Re: New directions in C: Default arguments raltbos@xs4all.nl (Richard Bos) - 2015-03-16 13:47 +0000
        Re: New directions in C: Default arguments David Brown <david.brown@hesbynett.no> - 2015-03-16 13:20 +0100
        Re: New directions in C: Default arguments fir <profesor.fir@gmail.com> - 2015-03-16 10:43 -0700
      Re: New directions in C: Default arguments David Brown <david.brown@hesbynett.no> - 2015-03-17 13:18 +0100
  Re: New directions in C: Default arguments bert <bert.hutchings@btinternet.com> - 2015-03-15 08:25 -0700
    Re: New directions in C: Default arguments jacob navia <jacob@spamsink.net> - 2015-03-15 18:16 +0100
  Re: New directions in C: Default arguments Michael Angelo Ravera <maravera@prodigy.net> - 2015-03-16 00:38 -0700
    Re: New directions in C: Default arguments fir <profesor.fir@gmail.com> - 2015-03-16 01:03 -0700
    Re: New directions in C: Default arguments Robert Wessel <robertwessel2@yahoo.com> - 2015-03-16 09:04 -0500
      Re: New directions in C: Default arguments Michael Angelo Ravera <maravera@prodigy.net> - 2015-03-17 00:22 -0700
        Re: New directions in C: Default arguments fir <profesor.fir@gmail.com> - 2015-03-17 01:08 -0700
          Re: New directions in C: Default arguments fir <profesor.fir@gmail.com> - 2015-03-19 01:37 -0700
            Re: New directions in C: Default arguments asetofsymbols@gmail.com - 2015-03-20 00:45 -0700
        Re: New directions in C: Default arguments Robert Wessel <robertwessel2@yahoo.com> - 2015-03-17 22:17 -0500
          Re: New directions in C: Default arguments Michael Angelo Ravera <maravera@prodigy.net> - 2015-03-18 15:55 -0700
  Re: New directions in C: Default arguments gwowen <gwowen@gmail.com> - 2015-03-16 01:07 -0700
    Re: New directions in C: Default arguments Keith Thompson <kst-u@mib.org> - 2015-03-16 08:18 -0700
      Re: New directions in C: Default arguments Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-03-16 17:35 +0000
      Definitions vs. Prototypes (Was: New directions in C: Default arguments) gazelle@shell.xmission.com (Kenny McCormack) - 2015-03-16 17:55 +0000
  Re: New directions in C: Default arguments Kaz Kylheku <kaz@kylheku.com> - 2015-03-16 20:21 +0000
    Re: New directions in C: Default arguments jacob navia <jacob@spamsink.net> - 2015-03-16 22:44 +0100

csiph-web