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UNIVERSAL - base class for ALL classes (blessed references)


$io = $fd->isa("IO::Handle");
$sub = $obj->can('print');

$yes = UNIVERSAL::isa($ref, "HASH");


UNIVERSAL is the base class which all bless references will inherit from, see perlobj

UNIVERSAL provides the following methods

isa ( TYPE )

isa returns true if REF is blessed into package TYPE or inherits from package TYPE.

isa can be called as either a static or object method call.

can ( METHOD )

can checks if the object has a method called METHOD. If it does then a reference to the sub is returned. If it does not then undef is returned.

can can be called as either a static or object method call.


VERSION will return the value of the variable $VERSION in the package the object is blessed into. If REQUIRE is given then it will do a comparison and die if the package version is not greater than or equal to REQUIRE.

VERSION can be called as either a static or object method call.

The isa and can methods can also be called as subroutines


isa returns true if one of the following statements is true.

  • VAL is a reference blessed into either package TYPE or a package which inherits from package TYPE.

  • VAL is a reference to a TYPE of Perl variable (e.g. 'HASH').

  • VAL is the name of a package that inherits from (or is itself) package TYPE.


If VAL is a blessed reference which has a method called METHOD, can returns a reference to the subroutine. If VAL is not a blessed reference, or if it does not have a method METHOD, undef is returned.

These subroutines should not be imported via use UNIVERSAL qw(...). If you want simple local access to them you can do

*isa = \&UNIVERSAL::isa;

to import isa into your package.