Testing for bless-edness in Perl

Published 2010-10-27

Using ref($o) to test whether $o is an object is obviously not enough, as it might be a simple unblessed reference. The following solution is almost perfect:


UNIVERSAL::can($o,'isa')

This tests if $o is a descendant of UNIVERSAL, where the isa method is defined.

However, the above is also true of classes! That is, in the following case, the condition is true:


package mypackage;
package clientcode;
if( UNIVERSAL::can('mypackage','isa') ){ ... }

As an aside, let me note that isa can also be called in a class context, which means that the following is also true:


package mypackage;
package clientcode;
$o = 'mypackage';
if( $o->isa('mypackage') ){ ... }

All in all, it seems the only reliable way of testing whether something is an object is to test whether it can 'isa' and to test whether it is a reference as well.

Tags: computing, Perl

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