Re: Possible to write compiler to Java VM?

macrakis@osf.org (Stavros Macrakis) writes:


|> There are some unsafe features in Ada other than the explicit ones.
|> For instance, aliasing is "erroneous" (thus allowing efficient
|> Fortran-style optimization of array code in subroutines), but no
|> runtime checking is required.


Not quite. Aliasing in itself has never been erroneous. In Ada 83,
forms of aliasing that caused the effect of a call to depend on the
parameter-passing mechanism were erroneous. In Ada 95, such aliasing
is no longer "erroneous"--meaning that the subsequent behavior of the
computation is undefined--but a "bounded error"--meaning the behavior
must be either that resulting from call-by-reference or that resulting
from copy-in-copy-out.


Uninitialized variables are a better example of a safety breach that
can occur even in an Ada program that does not explicitly use unsafe
features. The Normalize_Scalars pragma in the Ada-95 Safety and
Security annex is designed to increase the likelihood that an
uninitialized variable will raise the exception Constraint_Error
rather than corrupting the computation in unpredictable ways, so that
such errors can be smoked out during testing.


--
Norman H. Cohen ncohen@watson.ibm.com
--

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