Re: Attributes 'Version and 'Body_Version

[Keith Thompson <kst@cts.com>]

"Marin David Condic" <dont.bother.mcondic.auntie.spam@[acm.org> writes:
> On my way to playing around with something else, I started looking at the
> results of the attributes 'Version and 'Body_Version with Gnat 3.13p on
> WinNT. They appear to be intended for distributed systems, but could
> potentially be useful within any system that uses someone's library of
> stuff - a means of verifying that any assumed behavior from a given version
> is still valid. Or, for example, a means of recording the version of a
> package that produced some particular output so that on input, version
> differences can be accommodated.
> 
> Looking at the strings from a particular package (a generic instantiatiation
> at that) I see a pair of strings that look like: "2daafe2a" (spec)
> "21adf138" (body) I didn't encounter anything in the ARM indicating what the
> format of the string should be nor did I see anything in the GNAT documents
> that explained how to interpret the string. Obviously, this is going to be
> system dependent, but if you want to do anything more than say "This version
> isn't the one I remember" you need to know how to interpret the string. Has
> anybody used this before and possibly have some insight? Thanks.

If you want to know which version is "older" or "newer", I can't think
of any good way to define the concepts (other than perhaps the source
file timestamp, but that can be changed by copying the file).  Knowing
whether a version is older or newer than the one you expected might be
useful if you can assume upward compatibility, but that can't be
enforced by the language; compatibility can be upward, downward, both,
or neither, and may apply only to some features of a package.

If you're looking for a configuration management system, I suggest
using a configuration management system.  If you want a version
indication in your package that gives you more information than
equality/inequality, it should be easy enough to add one yourself.
(For example, if you use RCS or CVS, you can have a version string
that's automatically updated whenever the source file is checked in.)

The version strings used by GNAT look like they might be 32-bit
checksums of the source, in hexadecimal, but that's just a guess.

-- 
Keith Thompson (The_Other_Keith) kst@cts.com  <http://www.ghoti.net/~kst>
San Diego Supercomputer Center           <*>  <http://www.sdsc.edu/~kst>
Cxiuj via bazo apartenas ni.