Front page | perl.perl5.porters |
Postings from February 2021
There is an odd asymmetry with isa when testing if an object is derived
from its reference type:
my $aref = [ 1, 2, 3 ];
$aref isa ARRAY # is false
my $aobj = bless [ 5, 6, 7 ], "MyArray::Class";
$aobj isa MyArray::Class # is true
$aobj isa ARRAY # is true(!)
As further explained by documentation I have just added in my new
branch https://github.com/Perl/perl5/tree/leonerd/doc-isa
This is done in order to preserve the equivalence to the
C<UNIVERSAL::isa> method, which would also yield true in the same
circumstance. Despite this, it is not true that C<$aobj> would
consider methods in the C<ARRAY::> package as part of its method
resolution order.
I'm not terribly comfortable with this situation, but annoyingly any
other solution feels worse:
1. `isa` could warn (or croak?) on attempts to test the known all-caps
reftype names (which are NOT perl packages)
2. `isa` could specifically omit these (and thus break equivalence
with the `->isa` method)
Or something else.
If we accept that the current behaviour is the "least bad" of them and
we don't want to change it, then perhaps we can decide to
de-experimentalize this operator now it's been sitting unchanged for
all of 5.32, in time for a proper addition into 5.34.
Thoughts, anyone?
(cross-posted to github https://github.com/Perl/perl5/issues/18585)
--
Paul "LeoNerd" Evans
leonerd@leonerd.org.uk | https://metacpan.org/author/PEVANS
http://www.leonerd.org.uk/ | https://www.tindie.com/stores/leonerd/
Thread Next