Flashnux

GNU/Linux man pages

Livre :
Expressions régulières,
Syntaxe et mise en oeuvre :

ISBN : 978-2-7460-9712-4
EAN : 9782746097124
(Editions ENI)

GNU/Linux

RedHat 9.0

(Shrike)

UNIVERSAL(3pm)
UNIVERSAL

UNIVERSAL

NAME
SYNOPSIS
DESCRIPTION

NAME

UNIVERSAL − base class for ALL classes (blessed references)

SYNOPSIS 

    $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" ;
    $ver = VERSION $obj ;

DESCRIPTION

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

"UNIVERSAL" provides the following methods and functions:
$obj−>isa( TYPE ), CLASS− >isa( TYPE ), isa( VAL , TYPE )

    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

When used as an instance or class method ("$obj−"isa( TYPE )>), "isa" returns true if $obj is blessed into package "TYPE" or inherits from package "TYPE".

When used as a class method ("CLASS−"isa( TYPE )>; sometimes referred to as a static method), "isa" returns true if "CLASS" inherits from (or is itself) the name of the package "TYPE" or inherits from package "TYPE".

When used as a function, like

   use UNIVERSAL qw( isa ) ;
   $yes = isa $h, "HASH";
   $yes = isa "Foo", "Bar";

or

   require UNIVERSAL ;
   $yes = UNIVERSAL::isa $a, "ARRAY";

, "isa" returns true in the same cases as above and also if "VAL" is an unblessed reference to a perl variable of type "TYPE", such as " HASH ", " ARRAY ", or "Regexp".

$obj−>can( METHOD ), CLASS− >can( METHOD ), can( VAL , METHOD )

"can" checks if the object or class has a method called "METHOD". If it does then a reference to the sub is returned. If it does not then undef is returned. This includes methods inherited or imported by $obj, "CLASS", or "VAL".

"can" cannot know whether an object will be able to provide a method through AUTOLOAD , so a return value of undef 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 AUTOLOAD . For such ’dummy’ subs, "can" will still return a code reference, which, when called, will fall through to the AUTOLOAD . If no suitable AUTOLOAD is provided, calling the coderef will cause an error.

"can" can be called as a class (static) method, an object method, or a function.

When used as a function, if "VAL" is a blessed reference or package name 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.

VERSION ( [ REQUIRE ] )

"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 class (static) method, an object method or or a function.

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.

UNIVERSAL(3pm)