Re: Why no exception hierarchy ?

[dewar@cs.nyu.edu (Robert Dewar)]

The rationale for not having a hierarchy of exceptions is simply simplicity.
We looked at proposals for such extensions early on (see some of the arly
mapping documents for details), but decided that the complexity was not
worth it. There really is no problem with numeric_error and constraint_error
except that the original language goofed in trying to distinguish exception
conditions too finely, as became apparent later on. The current definition
is just a kludge for backwards compatibility, really no Ada 95 programmer
should even know about Numeric_Error.

The overuse of exceptions, and in particular the over specification of
fine distinctions in exceptions is a common design error in Ada programs,
which would no doubt be encouraged by a fancier exception mechanism.

For example, in one early version of the Posix interface, every error
condition was mapped into a separate exception, but it becamse clear that
it is much better to have a single exception with an error code.

When Jean considered this particular point (the Posix point), he wondered
to me whether perhaps a better language design would have been to have only
one exception with an error code ...