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 the perlobj manpage
UNIVERSAL provides the following methods
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 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 the first argument is a reference and either of the following statements
is true.
VAL is a blessed reference and is blessed into package TYPE
or inherits from package TYPE
VAL is a reference to a TYPE of perl variable (er
'HASH')
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.
If rather than formatting bugs, you encounter substantive content errors in these documents, such as mistakes in the explanations or code, please use the perlbug utility included with the Perl distribution.