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Rose::Object::MakeMethUser3Contributed Perl DocumeRose::Object::MakeMethods(3)

       Rose::Object::MakeMethods - A simple method maker base class.

	 package MyMethodMaker;

	 use Rose::Object::MakeMethods;
	 our @ISA = qw(Rose::Object::MakeMethods);

	 sub widget
	   my($class, $name, $args) = @_;

	   my $key = $args->{'hash_key'} || $name;
	   my $interface = $args->{'interface'}	|| 'get_set';

	   my %methods;

	   if($interface =~ /^get_set/)
	     $methods{$name} = sub
	       my($self) = shift;
	       if(@_) {	... }
	       return $self->{$key};

	   if($interface eq 'get_set_delete')
	     $methods{"delete_$name"} =	sub { ... };

	   return \%methods;

	 package MyObject;

	 sub new { ... }

	 use MyMethodMaker
	   'widget --get_set_delete' =>	'foo',

	   'widget' =>

	 $o = MyObject->new;


	 print $o->bar . $o->baz;

       Rose::Object::MakeMethods is the	base class for a family	of method
       makers. A method	maker is a module that's used to define	methods	in
       other packages. The actual method makers	are subclasses of
       Rose::Object::MakeMethods that define the names and options of the
       different kinds of methods that they can	make.

       There are method	makers that make both object methods and class
       methods.	The object method makers are in	the
       "Rose::Object::MakeMethods::*" namespace. The class method makers are
       in the "Rose::Class::MakeMethods::*" namespace for the sake of clarity,
       but still inherit from Class::MethodMaker and therefore share the same
       method making interface.

       Several useful method makers are	included under the
       "Rose::Object::MakeMethods::*" and "Rose::Class::MakeMethods::*"
       namespaces, mostly for use by other "Rose::*" objects and classes.

       This family of modules is not as	powerful or flexible as	the one	that
       inspired	it: Class::MethodMaker.	 I found that I	was only using a tiny
       corner of the functionality provided by Class::MethodMaker, so I	wrote
       this as a simple, smaller replacement.

       The fact	that many "Rose::*" modules use	Rose::Object::MakeMethods
       subclasses to make their	methods	should be considered an	implementation
       detail that can change at any time.

       allow_apparent_reload [BOOL]
	   Get or set an attribute that	determines whether or not to allow an
	   attempt to re-make the same method using the	same class that	made
	   it earlier.	The default is true.

	   This	issue comes up when a module is	forcibly reloaded, e.g., by
	   Apache::Reload or Apache::StatINC.  When this happens, all the
	   "make methods" actions will be attempted again.  In the absence of
	   the "preserve_existing" or "override_existing" options, the
	   allow_apparent_reload attribute will	be consulted.  If it's true,
	   and if it appears that the method in	question was made by this
	   method-maker	class, then it behaves as if the "preserve_existing"
	   option had been passed.  If it is false, then a fatal "method
	   redefined" error will occur.

       import SPEC
	   The "import"	class method is	mean to	be called implicitly as	a
	   result of a "use" statement.	 For example:

	       use Rose::Object::MakeMethods::Generic

	   is roughly equivalent to:

	       require Rose::Object::MakeMethods::Generic;

	   where SPEC is a series of specifications for	the methods to be
	   created. (But don't call import explicitly; use make_methods

	   In response to each method specification, one or more methods are

	   The first part of the SPEC argument is an optional hash reference
	   whose contents are intended to modify the behavior of the method
	   maker class itself, rather than the individual methods being	made.
	   There are currently only two	valid arguments	for this hash:

	   target_class	CLASS
	       Specifies that class that the methods will be added to.
	       Defaults	to the class from which	the call was made.  For
	       example,	this:

		   use Rose::Object::MakeMethods::Generic
		     { target_class => 'Foo' },

	       Is equivalent to	this:

		   package Foo;

		   use Rose::Object::MakeMethods::Generic

	       In general, the "target_class" argument is omitted since
	       methods are usually indented to end up in the class of the

	   override_existing BOOL
	       By default, attempting to create	a method that already exists
	       will result in a	fatal error.  But if the "override_existing"
	       option is set to	a true value, the existing method will be
	       replaced	with the generated method.

	   preserve_existing BOOL
	       By default, attempting to create	a method that already exists
	       will result in a	fatal error.  But if the "preserve_existing"
	       option is set to	a true value, the existing method will be left
	       unmodified.  This option	takes precedence over the
	       "override_existing" option.

	   After the optional hash reference full off options intended for the
	   method maker	class itself, a	series of method specifications	should
	   be provided.	 Each method specification defines one or more named
	   methods. The	components of such a specification are:

	   o   The Method Type

	       This is the name	of the subroutine that will be called in order
	       to generated the	methods	(see SUBCLASSING for more
	       information).  It describes the nature of the generated method.
	       For example, "scalar", "array", "bitfield", "object"

	   o   Method Type Arguments

	       Name/value pairs	that are passed	to the method maker of the
	       specified type in order to modify its behavior.

	   o   Method Names

	       One or more names for the methods that are to be	created.  Note
	       that a method maker of a	particular type	may choose to modify
	       or ignore these names.  In the common case, for each method
	       name argument, a	single method is created with the same name as
	       the method name argument.

	   Given the method type "bitfield" and	the method arguments "opt1"
	   and "opt2", the following examples show all valid forms for method
	   specifications, with	equivalent forms grouped together.

	   Create a bitfield method named "my_bits":

	      bitfield => 'my_bits'

	      bitfield => [ 'my_bits' ],

	      bitfield => [ 'my_bits' => {} ],

	   Create a bitfield method named "my_bits", passing the "opt1"
	   argument with a value of 2.

	      'bitfield	--opt1=2' => 'my_bits'

	      'bitfield	--opt1=2' => [ 'my_bits' ]

	      bitfield => [ 'my_bits' => { opt1	=> 2 } ]

	   Create a bitfield method named "my_bits", passing the "opt1"
	   argument with a value of 2 and the "opt2" argument with a value of

	      'bitfield	--opt1=2 --opt2=7' => 'my_bits'

	      'bitfield	--opt1=2 --opt2=7' => [	'my_bits' ]

	      bitfield => [ 'my_bits' => { opt1	=> 2, opt2 => 7	} ]

	      'bitfield	--opt2=7' => [ 'my_bits' => { opt1 => 2	} ]

	   In the case of a conflict between the options specified with	the
	   "--name=value" syntax and those provided in the hash	reference, the
	   ones	in the hash reference take precedence.	For example, these are

	      'bitfield	--opt1=99' => 'my_bits'

	      'bitfield	--opt1=5' => [ 'my_bits' => { opt1 => 99 } ]

	   If no value is provided for the first option, and if	it is
	   specified using the "--name"	syntax,	then it	is taken as the	value
	   of the "interface" option.  That is,	this:

	       'bitfield --foobar' => 'my_bits'

	   is equivalent to these:

	       'bitfield --interface=foobar' =>	'my_bits'

	       bitfield	=> [ my_bits =>	{ interface => 'foobar'	} ]

	   This	shortcut supports the convention that the "interface" option
	   is used to decide which set of methods to create.  But it's just a
	   convention; the "interface" option is no different from any of the
	   other options when it is eventually passed to the method maker of a
	   given type.

	   Any option other than the very first	that is	specified using	the
	   "--name" form and that lacks	an explicit value is simply set	to 1.
	   That	is, this:

	       'bitfield --foobar --baz' => 'my_bits'

	   is equivalent to these:

	       'bitfield --interface=foobar --baz=1' =>	'my_bits'

	       bitfield	=>
		 my_bits => { interface	=> 'foobar', baz => 1 }

	   Multiple method names can be	specified simultaneously for a given
	   method type and set of options.  For	example, to create methods
	   named "my_bits[1-3]", all of	the same type and with the same
	   options, any	of these would work:

		'bitfield --opt1=2' =>

		bitfield =>
		  'my_bits1' =>	{ opt1 => 2 },
		  'my_bits2' =>	{ opt1 => 2 },
		  'my_bits3' =>	{ opt1 => 2 },

	   When	options	are provided using the "--name=value" format, they
	   apply to all	methods	listed inside the array	reference, unless
	   overridden. Here's an example of an override:

		'bitfield --opt1=2' =>
		  'my_bits3' =>	{ opt1 => 999 },

	   In this case, "my_bits1" and	"my_bits2" use "opt1" values of	2, but
	   "my_bits3" uses an "opt1" value of 999.  Also note that it's	okay
	   to mix bare method names ("my_bits1"	and "my_bits2")	with method
	   names that have associated hash reference options ("my_bits3"), all
	   inside the same array reference.

	   Finally, putting it all together, here's a full example using
	   several different formats.

	       use Rose::Object::MakeMethods::Generic
		 { override_existing =>	1 },

		 'bitfield' => [ qw(my_bits other_bits)	],

		 'bitfield --opt1=5' =>

		 'bitfield' =>
		   'd' => { opt2 => 7 },
		   'e' => { opt1 => 1 },
		   'f' => { }, # empty is okay too

	   In the documentation	for the	various	Rose::Object::MakeMethods
	   subclasses, any of the valid	forms may be used in the examples.

       make_methods SPEC
	   This	method is equivalent to	the "import" method, but makes the
	   intent of the code clearer when it is called	explicitly.  (The
	   "import" method is only meant to be called implicitly by "use".)

       In order	to make	a Rose::Object::MakeMethods subclass that can actually
       make some methods, simply subclass Rose::Object::MakeMethods and	define
       one subroutine for each method type you want to support.

       The subroutine will be passed three arguments when it is	called:

       o   The class of	the method maker as a string.  This argument is
	   usually ignored unless you are going	to call	some other class

       o   The method name.  In	the common case, a single method with this
	   name	is defined, but	you are	free to	do whatever you	want with it,
	   including ignoring it.

       o   A reference to a hash containing the	options	for the	method.

       The subroutine is expected to return a reference	to a hash containing
       name/code reference pairs.  Note	that the subroutine does not actually
       install the methods.  It	simple returns the name	of each	method that is
       to be installed,	along with references to the closures that contain the
       code for	those methods.

       This subroutine is called for each name in the method specifier.	 For
       example,	this would result in three separate calls to the "bitfield"
       subroutine of the "MyMethodMaker" class:

	   use MyMethodMaker
	     bitfield =>
	       'your_bits'  => { size => 32 },
	       'other_bits' => { size => 128 },

       So why not have the subroutine return a single code reference rather
       than a reference	to a hash of name.code reference pairs?	 There are two

       First, remember that the	name argument ("my_bits", "your_bits",
       "other_bits") may be modified or	ignored	by the method maker.  The
       actual names of the methods created are determined by the keys of the
       hash reference returned by the subroutine.

       Second, a single	call with a single method name argument	may result in
       the creation more than one method--usually a "family" of	methods.  For

	   package MyObject;

	   use MyMethodMaker
	     # creates add_book(), delete_book(), and books() methods
	     'hash --manip' => 'book',

	   $o =	MyObject->new(...);


	   print join("\n", map	{ $_->title } $o->books);


       Here, the "hash"	method type elected to create three methods by
       prepending "add_" and "delete_" and appending "s" to the	supplied
       method name argument, "book".

       Anything	not specified in this documentation is simply a	matter of
       convention.  For	example, the Rose::Object::MakeMethods subclasses all
       use a common set	of method options: "hash_key", "interface", etc.  As
       you read	their documentation, this will become apparent.

       Finally,	here's an example of a subclass	that makes scalar accessors:

	   package Rose::Object::MakeMethods::Generic;

	   use strict;
	   use Carp();

	   use Rose::Object::MakeMethods;
	   our @ISA = qw(Rose::Object::MakeMethods);

	   sub scalar
	     my($class,	$name, $args) =	@_;

	     my	%methods;

	     my	$key = $args->{'hash_key'} || $name;
	     my	$interface = $args->{'interface'} || 'get_set';

	     if($interface eq 'get_set_init')
	       my $init_method = $args->{'init_method'}	|| "init_$name";

	       $methods{$name} = sub
		 return	$_[0]->{$key} =	$_[1]  if(@_ > 1);

		 return	defined	$_[0]->{$key} ?	$_[0]->{$key} :
		   ($_[0]->{$key} = $_[0]->$init_method());
	     elsif($interface eq 'get_set')
	       $methods{$name} = sub
		 return	$_[0]->{$key} =	$_[1]  if(@_ > 1);
		 return	$_[0]->{$key};
	     else { Carp::croak	"Unknown interface: $interface"	}

	     return \%methods;

       It can be used like this:

	   package MyObject;

	   use Rose::Object::MakeMethods::Generic
	     scalar =>

	     'scalar --get_set_init' =>	'name',

	   sub init_name { 'Fred' }

	   $o =	MyObject->new(power => 5);

	   print $o->name; # Fred

	   $o->power(99) or die	$o->error;

       This is actually	a subset of the	code in	the actual
       Rose::Object::MakeMethods::Generic module.  See the rest	of the
       "Rose::Object::MakeMethods::*" and "Rose::Class::MakeMethods::*"
       modules for more	examples.

       John C. Siracusa	(

       Copyright (c) 2010 by John C. Siracusa.	All rights reserved.  This
       program is free software; you can redistribute it and/or	modify it
       under the same terms as Perl itself.

perl v5.24.1			  2010-11-11	  Rose::Object::MakeMethods(3)


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