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From: Noel Yap (noel.yap_at_[hidden])
Date: 2006-01-26 19:41:58

On 1/26/06, Rich Johnson <rjohnson_at_[hidden]> wrote:
> On Jan 26, 2006, at 11:58 AM, Noel Yap wrote:
> > Hmm, I've been thinking about this problem but from a different
> > perspective.
> >
> > First, some definitions:
> > - patch release: the new component is link and load compatible with
> > the old one; clients might need to relink or reload
> > - minor release: the new component is compile compatible with the old
> > one; clients might need to recompile
> > - major release: the new component isn't compatible with the old one;
> > clients might need to modify code
> >
> > Given the above, a mapping can be made of changes to source to one of
> > the above. I suppose if a component developer follows the above, one
> > could write a class that could easily figure out whether or not a
> > certain M.m.p update is backwards compatible with another.
> >
> > Also, what really counts are changes to header files. More
> > specifically, changes to published header files (ie header files that
> > are installed so as to be usable by other components).
> I LIKE the crispness of your functional definitions. They suggest
> that there may exist an algorithm determining the ''order'' of a change:
> - Any change in the interface base class is _at least_ a minor release.
> - Any change in an implementation derived class is _at most_ a patch
> release.
> - Any change in the semantics of the base class interface is _at
> least_ a major release.
> - Version stamp can probably be generated by configuration control
> (i.e. CVS);
> - Version stamp can probably be used as a _signature_ of the module's
> interface.

This is exactly my intention. The rub is that automatically
generating the release numbers requires a very good C++ parser.

> FWIW, a "compiler compatibility" is probably required when dealing
> with separately compiled modules.

You're right. I hadn't considered that. I'll add it to my list of
caveats. Oh, wait, it just occurred to me that I would take care of
this by encoding architecture, compiler, and compiler flags into the
installation directory name.

> Applying the definitions to dynamically loaded libraries where we're
> _always_ relinking; we come up with:
> - if patch release; accept
> - if minor release; reject (you _might_ scoot by with some changes;
> but why risk it?)
> - if major release; reject
> - if compiler incompatible; reject (of course).

The last two are synonymous under my scheme.

> Dynamically loaded modules could supply a ''well known'' C function
> to access their version stamp (or otherwise determine compatibility)
> prior to instantiating any dynamically allocated objects.

Hmm, I had assumed, probably incorrectly, that components would be
installed within a directory whose name encodes the release number.
For example, /my/component/1.0/{include,lib}. OTOH, deployment is
really orthogonal to this issue. Having a "reflective" function
within the component would help in, IMO, messy deployments (eg
installing everything in /usr/local).

> Now you've got me thinking....

Good. Now there're at least two people I know thinking about this my way :-)


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