package UNIVERSAL;
-our $VERSION = '1.03';
+our $VERSION = '1.11';
# UNIVERSAL should not contain any extra subs/methods beyond those
# that it exists to define. The use of Exporter below is a historical
# anything unless called on UNIVERSAL.
sub import {
return unless $_[0] eq __PACKAGE__;
+ return unless @_ > 1;
+ require warnings;
+ warnings::warnif(
+ 'deprecated',
+ 'UNIVERSAL->import is deprecated and will be removed in a future perl',
+ );
goto &Exporter::import;
}
=head1 SYNOPSIS
- $is_io = $fd->isa("IO::Handle");
- $is_io = Class->isa("IO::Handle");
+ $is_io = $fd->isa("IO::Handle");
+ $is_io = Class->isa("IO::Handle");
- $sub = $obj->can("print");
- $sub = Class->can("print");
+ $does_log = $obj->DOES("Logger");
+ $does_log = Class->DOES("Logger");
- $sub = eval { $ref->can("fandango") };
- $ver = $obj->VERSION;
+ $sub = $obj->can("print");
+ $sub = Class->can("print");
+
+ $sub = eval { $ref->can("fandango") };
+ $ver = $obj->VERSION;
# but never do this!
- $is_io = UNIVERSAL::isa($fd, "IO::Handle");
- $sub = UNIVERSAL::can($obj, "print");
+ $is_io = UNIVERSAL::isa($fd, "IO::Handle");
+ $sub = UNIVERSAL::can($obj, "print");
=head1 DESCRIPTION
=item C<$obj>
-is a blessed reference or a string containing a package name
+is a blessed reference or a package name
=item C<CLASS>
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 invocant with C<blessed> from L<Scalar::Util> first:
+check the invocand with C<blessed> from L<Scalar::Util> first:
use Scalar::Util 'blessed';
- if ( blessed( $obj ) && $obj->isa("Some::Class") {
+ if ( blessed( $obj ) && $obj->isa("Some::Class") ) {
...
}
+=item C<< $obj->DOES( ROLE ) >>
+
+=item C<< CLASS->DOES( ROLE ) >>
+
+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<< $obj->can( METHOD ) >>
=item C<< CLASS->can( METHOD ) >>
C<VAL>.
C<can> cannot know whether an object will be able to provide a method through
-AUTOLOAD (unless the object's class has overriden C<can> appropriately), so a
+AUTOLOAD (unless the object's class has overridden C<can> appropriately), so a
return value of I<undef> does not necessarily mean the object will not be able
to handle the method call. To get around this some module authors use a forward
declaration (see L<perlsub>) for methods they will handle via AUTOLOAD. For
You may call C<can> as a class (static) method or an object method.
-Again, the same rule about having a valid invocant applies -- use an C<eval>
+Again, the same rule about having a valid invocand applies -- use an C<eval>
block or C<blessed> if you need to be extra paranoid.
=item C<VERSION ( [ REQUIRE ] )>
C<VERSION> will return the value of the variable C<$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>.
+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 by default.
-You may request the import of all three functions (C<isa>, C<can>, and
-C<VERSION>), however it is usually harmful to do so. Please don't do this in
+You may request the import of three functions (C<isa>, C<can>, and C<VERSION>),
+B<but this feature is deprecated and will be removed>. Please don't do this in
new code.
For example, previous versions of this documentation suggested using C<isa> as
https://perl5.git.perl.org / perl5.git / blobdiff