Re: Attributes 'Version and 'Body_Version

[Keith Thompson <kst@cts.com>]

dewar@gnat.com (Robert Dewar) writes:
> Keith Thompson <kst@cts.com> wrote in message
> news:<yecbsiekzkl.fsf@king.cts.com>...
> > The version strings used by GNAT look like they might be
> > 32-bit checksums of the source
>                                 ^
>                           sources!!!!!
> 
> It's really important to realize that 'Version is nothing
> like the version number of the source file, it is the
> version of the OBJECT, not the source, and hence depends
> on a whole set of sources.

Here's the RM definition of the 'Version attribute, from E.3(3):

    P'Version     Yields a value of the predefined type String that
                  identifies the version of the compilation unit that
                  contains the declaration of the program unit.

And here's what 10.1(2) has to say about compilation units:

    The text of a program can be submitted to the compiler in one or
    more compilations.  Each compilation is a succession of
    compilation_units.  A compilation_unit contains either the
    declaration, the body, or a renaming of a program unit.  The
    representation for a compilation is implementation-defined.

It certainly looks to me as if 'Version applies to a compilation unit,
and a compilation unit is a part of the text of a program.  The
version of a compilation unit changes whenever the compilation unit
changes in a "semantically significant" way; the phrase "semantically
significant" is explicitly left undefined.

If unit A depends on unit B, a change in B can affect the object
generated for A even if the source of A is unchanged.  I don't see a
requirement for A'Version or A'Body_Version to change when this
happens, though I can see that such a requirement would be useful.

It's likely that I'm missing something obvious, but I don't know what
it is.

-- 
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.