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From:Konstantin Osipov Date:July 1 2009 2:28pm
Subject:Re: MySql coding style: Request for deprecation of UPPERCASE typedefs
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* Kristian Nielsen <knielsen@stripped> [09/06/29 19:14]:

> > Just to clarify, when we mention forward declarations here, we
> > are talking about forward declarations of *classes* only, not
> > variables, so the "extern int foo" is not an example of a
> > forward declaration we are considering. For functions and
> > variables, it is a requirement to use an include file.
> 
> Mats, could you describe what the benefits are of using forward
> declarations of structs/classes in place of #including the
> definition?
> 
> Clearly, self-references in structs (whether direct or
> recursive) require forward declarations, but otherwise?
> 
> It seems to me to be a simpler if code referencing struct/class
> FOO would always do so by including file_defining_FOO.h? What am
> I missing? I don't remember seeing this style much in C/C++
> code...

A good design is a design that well reflects requirements in the
structure of the computer program. In human language, 
when creating a component, a good engineer avoids
unnecessary dependencies as much as possible.

Inclusion with #include is a stronger dependency than inclusion 
with a forward declaration. Especially in C++, where 
your component becomes aware of such intricate parts of the
included component as private members of classes.
This is why forward declarations are preferred.

Most C++ engineers I met found this fact more or less
self-evident.
However, if you are really interested in the subject
I warmly recommend "Large-Scale C++ Software Design"
by John Lakos. This books represents the viewpoint
of no-unnecessary-dependencies camp very well.

-- 
Thread
MySql coding style: Request for deprecation of UPPERCASE typedefsTor Didriksen22 Jun
  • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsMats Kindahl22 Jun
    • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsMichael Widenius24 Jun
      • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsTor Didriksen25 Jun
        • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsMichael Widenius27 Jun
      • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsMats Kindahl25 Jun
        • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsMichael Widenius27 Jun
          • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsJay Pipes27 Jun
          • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsTor Didriksen29 Jun
          • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsMats Kindahl29 Jun
            • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsKristian Nielsen29 Jun
              • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsTor Didriksen30 Jun
                • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsMats Kindahl30 Jun
                • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsKristian Nielsen30 Jun
                  • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsTor Didriksen1 Jul
                    • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsKristian Nielsen1 Jul
                  • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsKonstantin Osipov1 Jul
              • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsKonstantin Osipov1 Jul
                • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsKristian Nielsen2 Jul
  • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsKonstantin Osipov22 Jun
    • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsRoy Lyseng22 Jun
      • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsTor Didriksen23 Jun
        • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsMats Kindahl23 Jun
          • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsTor Didriksen23 Jun
            • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsMats Kindahl23 Jun
              • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsMichael Widenius27 Jun
                • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsMats Kindahl30 Jun
            • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsMichael Widenius24 Jun
              • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsTor Didriksen25 Jun
                • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsJonas Oreland25 Jun
                  • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsDavi Arnaut25 Jun
                    • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsMichael Widenius27 Jun
                  • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsMichael Widenius27 Jun
                • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsJay Pipes25 Jun
                  • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsMats Kindahl25 Jun
                  • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsMichael Widenius27 Jun
                • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsMichael Widenius27 Jun
                  • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsMats Kindahl30 Jun
              • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsMats Kindahl25 Jun
                • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsMichael Widenius27 Jun
                  • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsJay Pipes27 Jun
                    • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsMichael Widenius30 Jun
                  • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsJay Pipes27 Jun
                    • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsMichael Widenius1 Jul
    • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsTor Didriksen23 Jun
  • Re: MySql coding style: Request for deprecation of UPPERCASEtypedefsSergei Golubchik22 Jun
    • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsTor Didriksen23 Jun
      • Re: MySql coding style: Request for deprecation of UPPERCASEtypedefsSergei Golubchik23 Jun
        • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsTor Didriksen23 Jun
  • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsAlex Esterkin1 Jul
    • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsTor Didriksen1 Jul
    • Re: MySql coding style: Request for deprecation of UPPERCASE typedefsKonstantin Osipov1 Jul