use UNIVERSAL qw(isa);
$yes = isa($ref, "HASH");
$io = $fd->isa("IO::Handle");
$sub = $obj->can('print');
UNIVERSAL provides the following methods
REF is blessed into package TYPE
or inherits from package TYPE.
isa can be called as either a static or object method call.
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.
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.
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.