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Re: New directions in C: Default arguments

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David Brown <david.brown@hesbynett.no> writes:
> On 16/03/15 16:35, Keith Thompson wrote:
[...]
>> One problem with keyword parameters is that C doesn't require consistent
>> parameter names in all declarations.  Parameter names are not part of
>> the "signature" of a function (because in current C they're irrelevant
>> to the caller).
>> 
>> For example, given a definition like:
>> 
>>     void func(int x, int y) { /* ... */ }
>> 
>> any of these declarations would be compatible:
>> 
>>     void func(int, int);
>>     void func(int x, int y);
>>     void func(int y, int x);
>> 
>> Probably the simplest rule (that would not break existing code) would be
>> to make named parameters consistent with the most recent visible
>> declaration.
>
> That's a simple rule, and means there is no longer any problem.  The
> only conceivable alternative is to insist that declarations are
> consistent - while I think that would be a great thing, it would break
> existing code to no useful purpose.  It would therefore be a fine
> optional warning feature for a compiler, but should not be part of the
> language.

I wouldn't say that there's "no longer any problem".

In current C, the parameter names are meaningless.  The C standard
presents the declaration of the fopen() function as:

    FILE *fopen(const char * restrict filename,
        const char * restrict mode);

but the implementation I use has:

    extern FILE *fopen (const char *__restrict __filename,
        const char *__restrict __modes) ;

which is perfectly valid.

Even if I had a compiler that supports named parameters, I couldn't
write:

    FILE *f = fopen(.filename = "foo.txt", .modes = "r");

Supporting named parameters in portable code would require library
providers to declare parameters consistently.  With this approach,
it would be many years before all implementations are updated to use
consistent parameter names, and code that uses the standard names
would fail to compile under some implementations.  The standard
library would be bad enough; other libraries could be worse.

I had been thinking that matching the most recent visible declaration
would be the best approach, but now I'm thinking that *if* named
parameters were to be added to the language, we'd need to add a
rule requiring names to be defined consistently.  (Presumably if
C had had named parameters from the beginning, this rule would
already have been in place.)  Having two visible declarations
that use different names would become a constraint violation.
A declaration that doesn't provide parameter names would mean you
couldn't used named parameters when calling it (or, perhaps, would no
longer be permitted).

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

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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

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