IP : 3.145.172.51Hostname : host45.registrar-servers.comKernel : Linux host45.registrar-servers.com 4.18.0-513.18.1.lve.2.el8.x86_64 #1 SMP Sat Mar 30 15:36:11 UTC 2024 x86_64Disable Function : None :) OS : Linux
PATH:
/
home/
../
./
./
bin/
../
share/
perl5/
Devel/
../
I18N/
../
Config/
../
UNIVERSAL.pm/
/
package UNIVERSAL;
our $VERSION = '1.13';
# UNIVERSAL should not contain any extra subs/methods beyond those # that it exists to define. The existence of import() below is a historical # accident that can't be fixed without breaking code.
# Make sure that even though the import method is called, it doesn't do # anything unless called on UNIVERSAL. sub import { return unless $_[0] eq __PACKAGE__; return unless @_ > 1; require Carp; Carp::croak("UNIVERSAL does not export anything"); }
1; __END__
=head1 NAME
UNIVERSAL - base class for ALL classes (blessed references)
# but never do this! $is_io = UNIVERSAL::isa($fd, "IO::Handle"); $sub = UNIVERSAL::can($obj, "print");
=head1 DESCRIPTION
C<UNIVERSAL> is the base class from which all blessed references inherit. See L<perlobj>.
C<UNIVERSAL> provides the following methods:
=over 4
=item C<< $obj->isa( TYPE ) >>
=item C<< CLASS->isa( TYPE ) >>
=item C<< eval { VAL->isa( TYPE ) } >>
Where
=over 4
=item C<TYPE>
is a package name
=item C<$obj>
is a blessed reference or a package name
=item C<CLASS>
is a package name
=item C<VAL>
is any of the above or an unblessed reference
=back
When used as an instance or class method (C<< $obj->isa( TYPE ) >>), C<isa> returns I<true> if $obj is blessed into package C<TYPE> or inherits from package C<TYPE>.
When used as a class method (C<< CLASS->isa( TYPE ) >>, sometimes referred to as a static method), C<isa> returns I<true> if C<CLASS> inherits from (or is itself) the name of the package C<TYPE> or inherits from package C<TYPE>.
If you're not sure what you have (the C<VAL> case), wrap the method call in an C<eval> block to catch the exception if C<VAL> is undefined.
If you want to be sure that you're calling C<isa> as a method, not a class, check the invocand with C<blessed> from L<Scalar::Util> first:
C<DOES> checks if the object or class performs the role C<ROLE>. A role is a named group of specific behavior (often methods of particular names and signatures), similar to a class, but not necessarily a complete class by itself. For example, logging or serialization may be roles.
C<DOES> and C<isa> are similar, in that if either is true, you know that the object or class on which you call the method can perform specific behavior. However, C<DOES> is different from C<isa> in that it does not care I<how> the invocand performs the operations, merely that it does. (C<isa> of course mandates an inheritance relationship. Other relationships include aggregation, delegation, and mocking.)
By default, classes in Perl only perform the C<UNIVERSAL> role, as well as the role of all classes in their inheritance. In other words, by default C<DOES> responds identically to C<isa>.
There is a relationship between roles and classes, as each class implies the existence of a role of the same name. There is also a relationship between inheritance and roles, in that a subclass that inherits from an ancestor class implicitly performs any roles its parent performs. Thus you can use C<DOES> in place of C<isa> safely, as it will return true in all places where C<isa> will return true (provided that any overridden C<DOES> I<and> C<isa> methods behave appropriately).
=item C<< $obj->can( METHOD ) >>
=item C<< CLASS->can( METHOD ) >>
=item C<< eval { VAL->can( METHOD ) } >>
C<can> checks if the object or class has a method called C<METHOD>. If it does, then it returns a reference to the sub. If it does not, then it returns I<undef>. This includes methods inherited or imported by C<$obj>, C<CLASS>, or C<VAL>.
C<can> cannot know whether an object will be able to provide a method through AUTOLOAD (unless the object's class has overridden C<can> appropriately), so a return value of I<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 L<perlsub>) for methods they will handle via AUTOLOAD. For such 'dummy' subs, C<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.
You may call C<can> as a class (static) method or an object method.
Again, the same rule about having a valid invocand applies -- use an C<eval> block or C<blessed> if you need to be extra paranoid.
=item C<VERSION ( [ REQUIRE ] )>
C<VERSION> will return the value of the variable C<$VERSION> in the package the object is blessed into. If C<REQUIRE> is given then it will do a comparison and die if the package version is not greater than or equal to C<REQUIRE>, or if either C<$VERSION> or C<REQUIRE> is not a "lax" version number (as defined by the L<version> module).
The return from C<VERSION> will actually be the stringified version object using the package C<$VERSION> scalar, which is guaranteed to be equivalent but may not be precisely the contents of the C<$VERSION> scalar. If you want the actual contents of C<$VERSION>, use C<$CLASS::VERSION> instead.
C<VERSION> can be called as either a class (static) method or an object method.
=back
=head1 WARNINGS
B<NOTE:> C<can> directly uses Perl's internal code for method lookup, and C<isa> uses a very similar method and cache-ing strategy. This may cause strange effects if the Perl code dynamically changes @ISA in any package.
You may add other methods to the UNIVERSAL class via Perl or XS code. You do not need to C<use UNIVERSAL> to make these methods available to your program (and you should not do so).
=head1 EXPORTS
None.
Previous versions of this documentation suggested using C<isa> as a function to determine the type of a reference:
The problem is that this code would I<never> call an overridden C<isa> method in any class. Instead, use C<reftype> from L<Scalar::Util> for the first case: