Generate simple case folding tables only if asked

[perl5.git] / lib / UNIVERSAL.pm

diff --git a/lib/UNIVERSAL.pm b/lib/UNIVERSAL.pm
index eee8306..d11b893 100644 (file)
--- a/lib/UNIVERSAL.pm
+++ b/lib/UNIVERSAL.pm
@@ -1,6 +1,6 @@
 package UNIVERSAL;
 
-our $VERSION = '1.03';
+our $VERSION = '1.06';
 
 # UNIVERSAL should not contain any extra subs/methods beyond those
 # that it exists to define. The use of Exporter below is a historical
@@ -15,6 +15,12 @@ require Exporter;
 # 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;
 }
 
@@ -27,18 +33,21 @@ UNIVERSAL - base class for ALL classes (blessed references)
 
 =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
 
@@ -65,7 +74,7 @@ is a package name
 
 =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>
 
@@ -98,6 +107,34 @@ check the invocant with C<blessed> from L<Scalar::Util> first:
       ...
   }
 
+=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 ) >>
@@ -128,19 +165,31 @@ block or C<blessed> if you need to be extra paranoid.
 C<VERSION> will return the value of the variable C<$VERSION> in the
 package the object is blessed into. If C<REQUIRE> is given then
 it will do a comparison and die if the package version is not
-greater than or equal to C<REQUIRE>.
+greater than or equal to C<REQUIRE>.  Both C<$VERSION> or C<REQUIRE>
+must be "lax" version numbers (as defined by the L<version> module)
+or C<VERSION> will die with an error.
 
 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