Re: "access constant" discriminant

[rod.chapman@praxis-cs.co.uk (Rod Chapman)]

tmoran@acm.org wrote in message news:<lnJ1a.50689$SD6.3473@sccrnsc03>...
> Can this be done?  How?

A great shame that it can't.  From the viewpoint of a static analysis
tool, this is dreadful, since access parameters don't specify whether
the referenced objected is intended to be referenced, updated, or both - this
severely limits our ability to do information flow analysis in the presence
of access parameters, which needs
such information to be available as part of a subprogram's specifiction
if it to used usefully and efficiently implemented.  In light of this, SPARK
currently excludes access parameters.

(In SPARK, we have parameter modes as normal, but we extend a subprogram's
specification to include a list of all global data and their import/export
modes via the global annotation.  This makes IFA efficient, since we don't
need to look inside the body - all the info we need is on the spec.)

If access parameters were allowed to specify such information (e.g. "access in",
"access out" and "access in out") this would be a great help.  I remember
mentioning this to Tucker at SigAda and he took a note of it - not
sure if this issue has made it into any of the current AI's, though...

  - Rod