On 4/27/07, via RT Jerry Gay <[EMAIL PROTECTED]> wrote:
# New Ticket Created by Jerry Gay
# Please include the string: [perl #42776]
# in the subject line of all future correspondence about this issue.
# <URL: http://rt.perl.org/rt3/Ticket/Display.html?id=42776 >
there are two 'isa' ops, defined in src/ops/object.ops
one takes a string param, and the other a pmc. it seems the string
variant is used frequently throughout the source and tests, but the
pmc variant is much less frequently used, and i haven't come across
any tests, either. it seems these two ops don't agree on return
value... which is problematic.
D:\usr\local\parrot\head>parrot -
.sub main
.local pmc class, obj
class = new 'Class'
obj = class.'new'()
$I0 = isa obj, 'Object'
print $I0
.local pmc cl
cl = new 'String'
cl = 'Object'
$I1 = isa obj, cl
print $I1
.end
^Z
10
why? iunno. but this is causing me problems when using 'isa_ok' in
'Test/More.pir', since it uses the pmc variant.
It looks like the PMC variant is correct in this case, because Object
isn't actually a class. There's a class flag for PMCs that sets
whether or not they are a class and Object doesn't have this set.
When you call the PMC variant of isa, it calls Parrot_object_isa, and
that has this code:
/* if this is not a class */
if (!PObj_is_class_TEST(pmc)) {
pmc = VTABLE_get_class(interp, pmc);
}
So since Object isn't a class, it calls the get_class vtable and gets
the Class pmc. It then tests the object to see if it's a Class, which
it obviously isn't.
Contrast this to the String isa variant. It calls the isa vtable
function. Object inherits whatever default isa implementation is
provided. I'm not sure where that code is (it's a little harder to
find), but I'm guessing it just does a string comparison on the PMC
names without testing if the PMC is a class.
--
Matt Diephouse
http://matt.diephouse.com
