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Re: Refreshed genx.h, plus some plans

• To: xml-dev@l...
• Subject: Re: Refreshed genx.h, plus some plans
• From: Joe English <jenglish@f...>
• Date: Sat, 24 Jan 2004 19:39:32 -0800
• In-reply-to: <F30B3698-4ED5-11D8-B206-000A95A51C9E@t...>
• References: <F30B3698-4ED5-11D8-B206-000A95A51C9E@t...> <4D05972C-4ED1-11D8-B206-000A95A51C9E@t...> <200401250024.i0P0O2NK093024@a...> <200401250120.i0P1Keo25470@d...>

Tim Bray wrote:

> On Jan 24, 2004, at 5:20 PM, Joe English wrote:
> [on the subject of 'const']
> > Even if you don't consider it useful, it's a good idea
> > to make interfaces const-correct anyway just to avoid
> > impedance mismatches with other parts of the system.
>
> Using const variables means is that I have to cast the bloody variables
> every time I want to call strcpy() or sprintf() or any other bloody
> thing.  Which substantially uglifies the code.  -Tim


Hm, that doesn't sound right.  The only time const-correctness
uglifies code in that way is when you need to pass const objects
to an interface that's *not* const-correct.

If you make genx const-correct, you shouldn't encounter any
const-related ugliness in the implementation, as long as it
only relies on other const-correct interfaces (which strcpy(),
sprintf(), et al., most certainly are unless you've got a
broken compiler).

If OTOH the genx interface is *not* const-correct, you'll impose
the ugliness on *users* of the API who get data from a const-correct
library and need to pass it into yours.

Concrete example: if you declare

    int genxComment(genxWriter w, const utf8Byte * text);

then a user of the genx API can pass either a 'const utf8Byte *'
or a plain 'utf8Byte *' to the routine, without any compiler
warnings.

genxComment() in turn can pass 'text' to strcpy (as the second
argument), etc., also without any compiler warnings.  [*]

Conversely, if you declare:

    int genxComment(genxWriter w, utf8Byte * text);

then users of the API can *only* pass plain, non-const 'utf8Byte *'s
to the routine.  If they happen to have a 'const utf8Byte *',
then *they* need to do a cast, or copy to a non-const buffer,
or perform some other gyration.

So if genxComment() does not, in fact, write into 'text', declaring
it 'const' is a win.


--Joe English

  jenglish@f...


[*] Of course if genxComment() passes 'text' to strcpy() as the
    *first* argument, it *will* get a warning -- but if it does
    that then the 'text' parameter shouldn't have been declared
    'const' in the first place.

• Follow-Ups:
  • Re: Refreshed genx.h, plus some plans
    • From: David Tolpin <dvd@d...>

• References:
  • Re: Refreshed genx.h, plus some plans
    • From: Tim Bray <tbray@t...>
  • Re: Refreshed genx.h, plus some plans
    • From: Tim Bray <tbray@t...>
  • Re: Refreshed genx.h, plus some plans
    • From: David Tolpin <dvd@d...>
  • Re: Refreshed genx.h, plus some plans
    • From: Joe English <jenglish@f...>

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