Checking if an object inherits from class T

[Koszalek Opalek]

I am using objects of class T and objects of
other classes that inherit from T. Somewhere
in my code I need to check if an object is of
class T or of any other class that inherits
from T.

The following
if( ref $obj eq 'T' )
(obviously) works only for objects of class T but
not for objects blessed to other classes that
inherit from T.


I have come up with two solutions:

1) add the following method to T:
sub isT {};
and then check
if ( $obj->can( 'isT' )

This works except that it is two times slower
that checking the ref (i.e. if (ref $obj eq 'T'. )


2) add a field isT to the object in the constructor
and than check
if ( $obj->{isT} )
This is as fast as checking the ref but it looks
ugly and duplicates the field across all objects.


Is there a more elegant way that would be as fast
as checking the ref?


Koszalek

 

[Ben Morrow]

You can use Class->isa() (see "perldoc UNIVERSAL"):

if( ref($obj)->isa('T') )
{
# class is T or inherits from it
}

*NO*. Use $obj->isa('T') directly, otherwise objects can't override it
if they need to.

Ben

 

[brian d foy]

You can use Class->isa() (see "perldoc UNIVERSAL"):

if( ref($obj)->isa('T') )
{
# class is T or inherits from it
}

actaully, you want to do

if( eval { $obj->isa("T") } )

Call isa() directly on the object, and don't care too much about what
is actaully in $obj. If it's not an object, you just get back false,
which is still the right nswer to the question.

 

[Koszalek Opalek]

actaully, you want to do

   if( eval { $obj->isa("T") } )

Call isa() directly on the object, and don't care too much about what
is actaully in $obj. If it's not an object, you just get back false,
which is still the right nswer to the question.

I fixed my code and then bumped in this very problem
(i.e. Can't call method "isa" without a package or object
reference). I come to perl.misc and there is an answer
before I even asked the question .

K.

 

[Koszalek Opalek]

actaully, you want to do

if( eval { $obj->isa("T") } )

Call isa() directly on the object, and don't care too much about what
is actaully in $obj. If it's not an object, you just get back false,
which is still the right nswer to the question.

The only thing is that it is approximately 4x slower on my
simple benchmark compared to just checking the ref, i.e.
if( ref $obj eq 'T' )

But that's the way it has to stay.

K.