.\" Automatically generated by Pod::Man v1.34, Pod::Parser v1.13
.\"
.\" Standard preamble:
.\" ========================================================================
.de Sh \" Subsection heading
.br
.if t .Sp
.ne 5
.PP
\fB\\$1\fR
.PP
..
.de Sp \" Vertical space (when we can't use .PP)
.if t .sp .5v
.if n .sp
..
.de Vb \" Begin verbatim text
.ft CW
.nf
.ne \\$1
..
.de Ve \" End verbatim text
.ft R
.fi
..
.\" Set up some character translations and predefined strings.  \*(-- will
.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left
.\" double quote, and \*(R" will give a right double quote.  | will give a
.\" real vertical bar.  \*(C+ will give a nicer C++.  Capital omega is used to
.\" do unbreakable dashes and therefore won't be available.  \*(C` and \*(C'
.\" expand to `' in nroff, nothing in troff, for use with C<>.
.tr \(*W-|\(bv\*(Tr
.ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p'
.ie n \{\
.    ds -- \(*W-
.    ds PI pi
.    if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
.    if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\"  diablo 12 pitch
.    ds L" ""
.    ds R" ""
.    ds C` ""
.    ds C' ""
'br\}
.el\{\
.    ds -- \|\(em\|
.    ds PI \(*p
.    ds L" ``
.    ds R" ''
'br\}
.\"
.\" If the F register is turned on, we'll generate index entries on stderr for
.\" titles (.TH), headers (.SH), subsections (.Sh), items (.Ip), and index
.\" entries marked with X<> in POD.  Of course, you'll have to process the
.\" output yourself in some meaningful fashion.
.if \nF \{\
.    de IX
.    tm Index:\\$1\t\\n%\t"\\$2"
..
.    nr % 0
.    rr F
.\}
.\"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.hy 0
.if n .na
.\"
.\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2).
.\" Fear.  Run.  Save yourself.  No user-serviceable parts.
.    \" fudge factors for nroff and troff
.if n \{\
.    ds #H 0
.    ds #V .8m
.    ds #F .3m
.    ds #[ \f1
.    ds #] \fP
.\}
.if t \{\
.    ds #H ((1u-(\\\\n(.fu%2u))*.13m)
.    ds #V .6m
.    ds #F 0
.    ds #[ \&
.    ds #] \&
.\}
.    \" simple accents for nroff and troff
.if n \{\
.    ds ' \&
.    ds ` \&
.    ds ^ \&
.    ds , \&
.    ds ~ ~
.    ds /
.\}
.if t \{\
.    ds ' \\k:\h'-(\\n(.wu*8/10-\*(#H)'\'\h"|\\n:u"
.    ds ` \\k:\h'-(\\n(.wu*8/10-\*(#H)'\`\h'|\\n:u'
.    ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'^\h'|\\n:u'
.    ds , \\k:\h'-(\\n(.wu*8/10)',\h'|\\n:u'
.    ds ~ \\k:\h'-(\\n(.wu-\*(#H-.1m)'~\h'|\\n:u'
.    ds / \\k:\h'-(\\n(.wu*8/10-\*(#H)'\z\(sl\h'|\\n:u'
.\}
.    \" troff and (daisy-wheel) nroff accents
.ds : \\k:\h'-(\\n(.wu*8/10-\*(#H+.1m+\*(#F)'\v'-\*(#V'\z.\h'.2m+\*(#F'.\h'|\\n:u'\v'\*(#V'
.ds 8 \h'\*(#H'\(*b\h'-\*(#H'
.ds o \\k:\h'-(\\n(.wu+\w'\(de'u-\*(#H)/2u'\v'-.3n'\*(#[\z\(de\v'.3n'\h'|\\n:u'\*(#]
.ds d- \h'\*(#H'\(pd\h'-\w'~'u'\v'-.25m'\f2\(hy\fP\v'.25m'\h'-\*(#H'
.ds D- D\\k:\h'-\w'D'u'\v'-.11m'\z\(hy\v'.11m'\h'|\\n:u'
.ds th \*(#[\v'.3m'\s+1I\s-1\v'-.3m'\h'-(\w'I'u*2/3)'\s-1o\s+1\*(#]
.ds Th \*(#[\s+2I\s-2\h'-\w'I'u*3/5'\v'-.3m'o\v'.3m'\*(#]
.ds ae a\h'-(\w'a'u*4/10)'e
.ds Ae A\h'-(\w'A'u*4/10)'E
.    \" corrections for vroff
.if v .ds ~ \\k:\h'-(\\n(.wu*9/10-\*(#H)'\s-2\u~\d\s+2\h'|\\n:u'
.if v .ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'\v'-.4m'^\v'.4m'\h'|\\n:u'
.    \" for low resolution devices (crt and lpr)
.if \n(.H>23 .if \n(.V>19 \
\{\
.    ds : e
.    ds 8 ss
.    ds o a
.    ds d- d\h'-1'\(ga
.    ds D- D\h'-1'\(hy
.    ds th \o'bp'
.    ds Th \o'LP'
.    ds ae ae
.    ds Ae AE
.\}
.rm #[ #] #H #V #F C
.\" ========================================================================
.\"
.IX Title "UNIVERSAL 3"
.TH UNIVERSAL 3 "2002-11-24" "perl v5.8.0" "Perl Programmers Reference Guide"
.SH "NAME"
UNIVERSAL \- base class for ALL classes (blessed references)
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\&    $is_io = $fd->isa("IO::Handle");
\&    $is_io = Class->isa("IO::Handle");
.Ve
.PP
.Vb 2
\&    $sub = $obj->can("print");
\&    $sub = Class->can("print");
.Ve
.PP
.Vb 4
\&    use UNIVERSAL qw( isa can VERSION );
\&    $yes = isa $ref, "HASH" ;
\&    $sub = can $ref, "fandango" ;
\&    $ver = VERSION $obj ;
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\f(CW\*(C`UNIVERSAL\*(C'\fR is the base class which all bless references will inherit from,
see perlobj.
.PP
\&\f(CW\*(C`UNIVERSAL\*(C'\fR provides the following methods and functions:
.IP "$obj\->isa( \s-1TYPE\s0 ), \s-1CLASS\-\s0>isa( \s-1TYPE\s0 ), isa( \s-1VAL\s0, \s-1TYPE\s0 )" 4
.IX Item "$obj->isa( TYPE ), CLASS->isa( TYPE ), isa( VAL, TYPE )"
.Vb 4
\&    C<TYPE> is a package name
\&    $obj is a blessed reference or a string containing a package name
\&    C<CLASS> is a package name
\&    C<VAL> is any of the above or an unblessed reference
.Ve
.Sp
When used as an instance or class method (\f(CW\*(C`$obj\-\*(C'\fRisa( \s-1TYPE\s0 )>), \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.
.Sp
When used as a class method (\f(CW\*(C`CLASS\-\*(C'\fRisa( \s-1TYPE\s0 )>; 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.
.Sp
When used as a function, like
.Sp
.Vb 3
\&   use UNIVERSAL qw( isa ) ;
\&   $yes = isa $h, "HASH";
\&   $yes = isa "Foo", "Bar";
.Ve
.Sp
or
.Sp
.Vb 2
\&   require UNIVERSAL ;
\&   $yes = UNIVERSAL::isa $a, "ARRAY";
.Ve
.Sp
, \f(CW\*(C`isa\*(C'\fR returns \fItrue\fR in the same cases as above and also if \f(CW\*(C`VAL\*(C'\fR is an
unblessed reference to a perl variable of type \f(CW\*(C`TYPE\*(C'\fR, such as \*(L"\s-1HASH\s0\*(R",
\&\*(L"\s-1ARRAY\s0\*(R", or \*(L"Regexp\*(R".
.IP "$obj\->can( \s-1METHOD\s0 ), \s-1CLASS\-\s0>can( \s-1METHOD\s0 ), can( \s-1VAL\s0, \s-1METHOD\s0 )" 4
.IX Item "$obj->can( METHOD ), CLASS->can( METHOD ), can( VAL, METHOD )"
\&\f(CW\*(C`can\*(C'\fR checks if the object or class has a method called \f(CW\*(C`METHOD\*(C'\fR. If it does
then a reference to the sub is returned. If it does not then \fIundef\fR is
returned.  This includes methods inherited or imported by \f(CW$obj\fR, \f(CW\*(C`CLASS\*(C'\fR, or
\&\f(CW\*(C`VAL\*(C'\fR.
.Sp
\&\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
will cause an error.
.Sp
\&\f(CW\*(C`can\*(C'\fR can be called as a class (static) method, an object method, or a
function.
.Sp
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.
.IP "\s-1VERSION\s0 ( [ \s-1REQUIRE\s0 ] )" 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.
.Sp
\&\f(CW\*(C`VERSION\*(C'\fR can be called as either a class (static) method, an object method or
or a function.
.PP
These subroutines should \fInot\fR be imported via \f(CW\*(C`use\ UNIVERSAL\ qw(...)\*(C'\fR.
If you want simple local access to them you can do
.PP
.Vb 1
\&  *isa = \e&UNIVERSAL::isa;
.Ve
.PP
to import isa into your package.