Catch exception objects in most-derived-first order .
The only drawback to using method calls to detect particular types of exceptions:
if ( X::TooBig->caught( ) ) {
is that you have to be careful about the order in which you try your alternatives. For example, if X::WaaaaayTooBig inherits from X:TooBig, the following code won't work correctly:
# If the attempt fails...if ($EVAL_ERROR) {# If the candidate was considered too big, go with the maximum allowed...if ( X::TooBig->caught( ) ) { my @range = $EVAL_ERROR->get_range( ); $value = $range[-1]; }# If the candidate was considered waaaaay too big, rethrow the exception...elsif ( X::WaaaaayTooBig->caught( ) ) { $EVAL_ERROR->rethrow( ); }# etc.}
The problem is that if an X::WaaaaayTooBig exception is thrown, $EVAL_ERROR will refer to an X::WaaaaayTooBig object. But the X::WaaaaayTooBig class inherits from the X::TooBig class, so an X::WaaaaayTooBig object
is an X::TooBig object. That means the first if test will succeed, and the specialized derived-class exception will be treated like a generic base-class exception instead.
The solution is simple: whenever you're determining the type of an exception you just caught, test for the most-derived classes first.