Re: Ada and Java. different behaviour. casting long to int problem.

[Robert Dewar <dewar@gnat.com>]

In article <FD85Lq.Hyp.0.-s@inmet.camb.inmet.com>,
  stt@houdini.camb.inmet.com (Tucker Taft) wrote:

> Ada is value-preserving, with a run-time check on overflow
> (note that GNAT in some configurations suppresses overflow
> checks by default,
> which is naughty in some people's view ;-).

There is no requirement that the "default" (whatever that
may mean) mode of an Ada compiler be the mode in which it
is standard compliant. The only requirement is that there
is a way of running the compiler that is standard compliant
(and of course the VSR for the validation says exactly which
set of switches were used for validation).

While one can argue about the choice of overflow checks off,
constraint checks on being the default, we strongly feel that
being standard compliant in other respects is quite the wrong
default. In particular, the rather dangerous dynamic approach
to elaboration checking that is mandated by the standard is
of course available in GNAT (using the -gnatE switch), but we
consider it considerably inferior to the default static
elaboration analysis which is the default mode. In this default
mode, the compiler can determine a guaranteed safe order of
elaboration for almost all cases, which is much better than
having to delay the checks till run time.

But in any case, an important rule is *read the documentation*
of whatever compiler you are using, and in particular be careful
to know what all the options available for compilation are.
GNAT has quite a long list of compilation switches, and many
of them are quite useful (for example, it is a very good idea
to use -gnatwu for nearly all compilations -- and if you don't
know what -gnatwu does, go look it up :-)

Robert Dewar
Ada Core Technologies


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