package UNIVERSAL;
-our $VERSION = '1.03';
+our $VERSION = '1.04';
# 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__;
+ 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>
...
}
+=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
+invocant 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 ) >>
=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