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.TH UNIVERSAL 3 "2001-09-21" "perl v5.8.8" "Perl Programmers Reference Guide"
UNIVERSAL \- base class for ALL classes (blessed references)
\& $is_io = $fd->isa("IO::Handle");
\& $is_io = Class->isa("IO::Handle");
\& $sub = $obj->can("print");
\& $sub = Class->can("print");
\& use UNIVERSAL qw( isa can VERSION );
\& $yes = isa $ref, "HASH" ;
\& $sub = can $ref, "fandango" ;
\&\f(CW\*(C`UNIVERSAL\*(C'\fR is the base class which all bless references will inherit from,
\&\f(CW\*(C`UNIVERSAL\*(C'\fR provides the following methods and functions:
.ie n .IP """$obj\->isa( TYPE )""" 4
.el .IP "\f(CW$obj\->isa( TYPE )\fR" 4
.IX Item "$obj->isa( TYPE )"
.ie n .IP """CLASS\->isa( TYPE )""" 4
.el .IP "\f(CWCLASS\->isa( TYPE )\fR" 4
.IX Item "CLASS->isa( TYPE )"
.ie n .IP """isa( VAL, TYPE )""" 4
.el .IP "\f(CWisa( VAL, TYPE )\fR" 4
.IX Item "isa( VAL, TYPE )"
is a blessed reference or a string containing a package name
.el .IP "\f(CWCLASS\fR" 4
is any of the above or an unblessed reference
When used as an instance or class method (\f(CW\*(C`$obj\->isa( TYPE )\*(C'\fR),
\&\f(CW\*(C`isa\*(C'\fR returns \fItrue\fR if \f(CW$obj\fR is blessed into package \f(CW\*(C`TYPE\*(C'\fR or
inherits from package \f(CW\*(C`TYPE\*(C'\fR.
When used as a class method (\f(CW\*(C`CLASS\->isa( TYPE )\*(C'\fR: sometimes
referred to as a static method), \f(CW\*(C`isa\*(C'\fR returns \fItrue\fR if \f(CW\*(C`CLASS\*(C'\fR
inherits from (or is itself) the name of the package \f(CW\*(C`TYPE\*(C'\fR or
inherits from package \f(CW\*(C`TYPE\*(C'\fR.
When used as a function, like
\& use UNIVERSAL qw( isa ) ;
\& $yes = isa $h, "HASH";
\& $yes = isa "Foo", "Bar";
\& $yes = UNIVERSAL::isa $a, "ARRAY";
\&\f(CW\*(C`isa\*(C'\fR returns \fItrue\fR in the same cases as above and also if \f(CW\*(C`VAL\*(C'\fR is an
unblessed reference to a perl variable of type \f(CW\*(C`TYPE\*(C'\fR, such as \*(L"\s-1HASH\s0\*(R",
\&\*(L"\s-1ARRAY\s0\*(R", or \*(L"Regexp\*(R".
.ie n .IP """$obj\->can( METHOD )""" 4
.el .IP "\f(CW$obj\->can( METHOD )\fR" 4
.IX Item "$obj->can( METHOD )"
.ie n .IP """CLASS\->can( METHOD )""" 4
.el .IP "\f(CWCLASS\->can( METHOD )\fR" 4
.IX Item "CLASS->can( METHOD )"
.ie n .IP """can( VAL, METHOD )""" 4
.el .IP "\f(CWcan( VAL, METHOD )\fR" 4
.IX Item "can( VAL, METHOD )"
\&\f(CW\*(C`can\*(C'\fR checks if the object or class has a method called \f(CW\*(C`METHOD\*(C'\fR. If it does
then a reference to the sub is returned. If it does not then \fIundef\fR is
returned. This includes methods inherited or imported by \f(CW$obj\fR, \f(CW\*(C`CLASS\*(C'\fR, or
\&\f(CW\*(C`can\*(C'\fR cannot know whether an object will be able to provide a method
through \s-1AUTOLOAD\s0, so a return value of \fIundef\fR does not necessarily mean
the object will not be able to handle the method call. To get around
this some module authors use a forward declaration (see perlsub)
for methods they will handle via \s-1AUTOLOAD\s0. For such 'dummy' subs, \f(CW\*(C`can\*(C'\fR
will still return a code reference, which, when called, will fall through
to the \s-1AUTOLOAD\s0. If no suitable \s-1AUTOLOAD\s0 is provided, calling the coderef
\&\f(CW\*(C`can\*(C'\fR can be called as a class (static) method, an object method, or a
When used as a function, if \f(CW\*(C`VAL\*(C'\fR is a blessed reference or package name which
has a method called \f(CW\*(C`METHOD\*(C'\fR, \f(CW\*(C`can\*(C'\fR returns a reference to the subroutine.
If \f(CW\*(C`VAL\*(C'\fR is not a blessed reference, or if it does not have a method
\&\f(CW\*(C`METHOD\*(C'\fR, \fIundef\fR is returned.
.ie n .IP """VERSION ( [ REQUIRE ] )""" 4
.el .IP "\f(CWVERSION ( [ REQUIRE ] )\fR" 4
.IX Item "VERSION ( [ REQUIRE ] )"
\&\f(CW\*(C`VERSION\*(C'\fR will return the value of the variable \f(CW$VERSION\fR in the
package the object is blessed into. If \f(CW\*(C`REQUIRE\*(C'\fR is given then
it will do a comparison and die if the package version is not
greater than or equal to \f(CW\*(C`REQUIRE\*(C'\fR.
\&\f(CW\*(C`VERSION\*(C'\fR can be called as either a class (static) method, an object
You may request the import of all three functions (\f(CW\*(C`isa\*(C'\fR, \f(CW\*(C`can\*(C'\fR, and
\&\f(CW\*(C`VERSION\*(C'\fR), however it isn't usually necessary to do so. Perl magically
makes these functions act as methods on all objects. The one exception is
\&\f(CW\*(C`isa\*(C'\fR, which is useful as a function when operating on non-blessed
projects / OpenSPARC-T2-SAM / blob