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MakeMethods::Docs::ExaUsersContributed Perl DocuMakeMethods::Docs::Examples(3)

NAME
       Class::MakeMethods::Docs::Examples - Sample Declarations	and Usage

EXAMPLES
       The following examples indicate some of the capabilities	of
       Class::MakeMethods.

   A Contrived Example
       Object-oriented Perl code is widespread -- you've probably seen code
       like the	below a	million	times:

	 my $obj = MyStruct->new( foo=>"Foozle", bar=>"Bozzle" );
	 if ( $obj->foo() =~ /foo/i ) {
	   $obj->bar("Barbados!");
	 }

       Here's a	possible implementation	for the	class whose interface is shown
       above:

	 package MyStruct;

	 sub new {
	   my $callee =	shift;
	   my $self = bless { @_ }, (ref $callee || $callee);
	   return $self;
	 }

	 sub foo {
	   my $self = shift;
	   if (	scalar @_ ) {
	     $self->{'foo'} = shift();
	   } else {
	     $self->{'foo'}
	   }
	 }

	 sub bar {
	   my $self = shift;
	   if (	scalar @_ ) {
	     $self->{'bar'} = shift();
	   } else {
	     $self->{'bar'}
	   }
	 }

       Class::MakeMethods allows you to	simply declare those methods to	be of
       a predefined type, and it generates and installs	the necessary methods
       in your package at compile-time.

       Here's the equivalent declaration for that same basic class:

	 package MyStruct;
	 use Class::MakeMethods::Standard::Hash	(
	   'new'       => 'new',
	   'scalar'    => 'foo',
	   'scalar'    => 'bar',
	 );

   A Typical Example
       The following example shows a common case of constructing a class with
       several types of	accessor methods

	 package MyObject;
	 use Class::MakeMethods::Standard::Hash	(
	   new => 'new',
	   scalar => [ 'foo', 'bar' ],
	   array => 'my_list',
	   hash	=> 'my_index',
	 );

       This class now has a constructor	named new, two scalar accessors	named
       foo and bar, and	a pair of reference accessors named my_list and
       my_index. Typical usage of the class might include calls	like the
       following:

	 my $obj = MyObject->new( foo => 'Foozle' );
	 print $obj->foo();

	 $obj->bar('Barbados');
	 print $obj->bar();

	 $obj->my_list(0 => 'Foozle', 1	=> 'Bang!');
	 print $obj->my_list(1);

	 $obj->my_index('broccoli' => 'Blah!', 'foo' =>	'Fiddle');
	 print $obj->my_index('foo');

   Lvalue Accessors
       The Template subclasses support an optional "--lvalue" modifer that
       causes your accessors method to be marked as returning an lvalue	which
       can be assigned to. (This feature is only available on Perl 5.6 or
       later.)

	 package MyStruct;
	 use Class::MakeMethods::Template::Hash	(
	   'new'		   => 'new',
	   'scalar --get --lvalue' => 'foo',
	   'array --get	--lvalue'  => 'bar',
	 );

	 $obj->foo = "Foozle";
	 print $obj->foo;

	 $obj->bar = ( 'baz', 'beep', 'boop' );
	 print $obj->bar->[1]; # beep

   String and Numeric Accessors
       In addition to the "scalar" accessor supported by the "Standard::*"
       classes,	the Template subclasses	also provide specialized accessors
       that can	facilitate the use of specific types of	data.

       For example, we could declare the following class to hold information
       about available Perl packages:

	 package MyVersionInfo;
	 use Class::MakeMethods::Template::Hash	(
	   'new'     =>	'new',
	   'string'  =>	'package',
	   'number'  =>	'version',
	 );

	 sub summary {
	   my $self = shift;
	   return $self->package() . " is at version " . $self->version()
	 }

       You could use this class	as follows:

	 package main;
	 use MyVersionInfo;

	 my $obj = MyVersionInfo->new( package=>"Class::MakeMethods");
	 $obj->version(	2.0 );
	 print $obj->summary();

       These accessors will provide a bit of diagnostic	type checking; an
       attempt to call "$obj->version("foo")" will cause your program to
       croak.

   String Concatenation	Interface
       The following defines a get_concat method "i", and specifies a string
       to use when joining additional values when this method is called.

	 use Class::MakeMethods::Template::Hash
	   'string' => [ '--get_concat', 'i', {	join =>	' - ' }	];

       (See Class::MakeMethods::Template::Generic for information about	the
       "string"	"get_concat" interface.)

   Access Control Example
       The following defines a secret_password method, which will croak	if it
       is called from outside of the declaring package.

	 use Class::MakeMethods::Composite::Hash
	   'scalar' => [ 'secret_password' => {	permit => 'pp' } ];

       (See Class::MakeMethods::Composite for information about	the "permit"
       modifier.)

       For template classes, the same thing is accomplished with '--private':

	 use Class::MakeMethods::Template::Hash
	   'scalar' => [ '--private', 'secret_password'	];

       (See Class::MakeMethods::Template::Universal for	information about the
       "private" modifier.)

   Lazy-Init Interface
       Templapte scalar	accessors declared with	the "init_and_get" interface
       can be used for "memoization" or	lazy-evaluation	for object attributes.
       If the current accessor value is	undefined, they	will first call	a
       user-provided init_* method and save its	value.

	 package MyWidget;
	 use Class::MakeMethods::Template::Hash	(
	   'new	--with_values' => [ 'new' ],
	   'scalar --init_and_get' => [	'foo', 'count',	'result' ],
	 );

	 sub init_foo {
	   return 'foofle';
	 }

	 sub init_count	{
	   return '3';
	 }

	 sub init_result {
	   my $self = shift;
	   return $self->foo x $self->count;
	 }
	 ...

	 my $widget = MyWidget->new();
	 print $widget->result;	# output: fooflefooflefoofle

	 # if values are predefined, the init methods are not used
	 my $other_widget = MyWidget->new( foo => 'bar', count => 2 );
	 print $widget->result;	# output: barbar

       (See Class::MakeMethods::Template::Generic for more information about
       "init_and_get". This interface is also supported	by all of Generic's
       subclasses, so you can add lazy-init methods for	global data, class
       data, array objects, etc. Unfortunately,	to date	it is only supported
       for scalar-value	accessors...)

   Helper Methods
       Template	methods	often include similarly-named "helper" methods.	For
       example,	specifying the "--with_clear" interface	for Template::*:scalar
       methods creates an extra	method for each	accessor x named clear_x.

	 package MyClass;
	 use Class::MakeMethods::Template::Hash('scalar	--with_clear' => 'foo');

	 my $obj = MyClass->new;
	 $obj->foo(23);
	 $obj->clear_foo;
	 print $obj->foo();

   Reference Accessor and Helper Methods
       For references to arrays	and hashes, the	Template subclasses provide
       accessors with extra "helper methods" to	facilitate method-based
       interaction.

       Here's a	class whose instances each store a string and an array
       reference, along	with a method to search	the directories:

	 package MySearchPath;
	 use Class::MakeMethods::Template::Hash	(
	   'new'     =>	'new',
	   'string'  =>	'name',
	   'array'   =>	'directories',
	 );

	 sub search {
	   my $self = shift;
	   my $target =	shift;
	   foreach my $dir ( $self->directories	) {
	     my	$candidate = $dir . '/'	. $target;
	     return $candidate if ( -e $candidate );
	   }
	   return;
	 }

       Note that the directories accessor returns the contents of the array
       when called in a	list context, making it	easier to loop over.

       And here's a sample usage:

	 package main;
	 use MySearchPath;

	 my $libs = MySearchPath->new( name=>"libs", directories=>['/usr/lib'] );
	 $libs->push_directories( '/usr/local/lib' );

	 print "Searching in " . $libs->count_directories() . "directories.\n";
	 foreach ( 'libtiff', 'libjpeg'	) {
	   my $file = $libs->search("$_.so");
	   print "Checking $_: " . ( $file || 'not found' ) . "\n";
	 }

       Note the	use of the push_* and count_* "helper" accessor	methods, which
       are defined by default for all 'Template::*:array' declarations.

       Consult Class::MakeMethods::Template::Generic for more information
       about the available types of reference accessors, and the various
       methods they define.

   Object Accessors
       There's also a specialized accessor for object references:

	 package MyStruct;
	 use Class::MakeMethods::Template::Hash	(
	   'new'    => 'new',
	   'object' => [ 'widget' => {class=>'MyWidgetClass', delegate=>"twiddle"} ],
	 );

       (Note that the "class" and "delegate" values specified above are	method
       parameters, which provide additional information	about the "widget"
       declaration; see	"Standard Declaration Syntax" for more information.)

       The above declaration creates methods equivalent	to the following:

	 package MyStruct;

	 sub widget {
	   my $self = shift;
	   if (	scalar @_ ) {
	     if	(ref $_[0] and UNIVERSAL::isa($_[0], 'MyWidgetClass')) {
	       $self->{widget} = shift;
	     } else {
	       $self->{widget} = MyWidgetClass->new(@_);
	     }
	   } else {
	     return $self->{widget};
	   }
	 }

	 sub clear_widget {
	   my $self = shift;
	   $self->{widget} = undef;
	 }

	 sub twiddle {
	   my $self = shift;
	   my $obj = $self->widget()
	     or	Carp::croak("Can't forward twiddle because widget is empty");
	   $obj->twiddle(@_)
	 }

   Mixing Object and Global Methods
       Here's a	package	declaration using two of the included subclasses,
       "Standard::Hash", for creating and accessing hash-based objects,	and
       "Basic::Global",	for simple global-value	accessors:

	 package MyQueueItem;

	 use Class::MakeMethods::Standard::Hash	(
	   new => { name => 'new', defaults=>{ foo => 'Foozle' } },
	   scalar => [ 'foo', 'bar' ],
	   hash	=> 'history'
	 );

	 use Class::MakeMethods::Basic::Global (
	   scalar => 'Debug',
	   array  => 'InQueue',
	 );

	 sub AddQueueItem {
	   my $class = shift;
	   my $instance	= shift;
	   $instance->history('AddQueueItem' =>	time());
	   $class->InQueue([0, 0], $instance);
	 }

	 sub GetQueueItem {
	   my $class = shift;
	   $class->InQueue([0, 1], []) or $class->new
	 }

   Adding Custom Initialization	to Constructors
       Frequently you'll want to provide some custom code to initialize	new
       objects of your class. Most of the *:new	constructor methods provides a
       way to ensure that this code is consistently called every time a	new
       instance	is created.

       Composite::Hash:new { post_rules	=> [] }
	   The Composite classes allow you to add pre- and post-operations to
	   any method, so you can pass in a code-ref to	be executed after the
	   new() method.

	     package MyClass;

	     sub new_post_init {
	       my $self	= ${(pop)->{result}}; #	get result of original new()
	       length($self->foo) or $self->foo('FooBar');   # default value
	       warn "Initialized new object '$self'";
	     }

	     use Class::MakeMethods (
	       'Composite::Hash:new' =>	[
		   'new' => { post_rules=>[ \&new_post_init ] }
	       ],
	       'Composite::Hash:scalar'	=> 'foo;,
	     );
	     ...
	     package main;
	     my	$self =	MyClass->new( foo => 'Foozle' )

       Template::Hash:new --and_then_init
	   Use 'Template::Hash:new --and_then_init', which will	first create
	   the object and initialize it	with the provided values, and then
	   call	an init() method on the	new object before returning it.

	     package MyClass;
	     use Class::MakeMethods::Template::Hash (
	       'new --and_then_init' =>	'new'
	       'string'	 => 'foo'
	     );
	     sub init {
	       my $self	= shift;
	       length($self->foo) or $self->foo('FooBar');   # default value
	       warn "Initialized new object '$self'";
	     }
	     ...
	     package main;
	     my	$self =	MyClass->new( foo => 'Foozle' )

       Template::Hash:new --with_init
	   If you don't	want your constructor to use the default hash-of-
	   method-names	style of initialization, use 'Template::Hash:new
	   --with_init', which will create an empty object, pass its arguments
	   to the init() method	on the new object, and then return it.

	     package MyClass;
	     use Class::MakeMethods::Template::Hash (
	       'new --with_init' => 'new'
	       'string'	 => 'foo'
	     );
	     sub init {
	       my $self	= shift;
	       $self->foo( shift || 'FooBar' );	# init with arg	or default
	       warn "Initialized new object '$self'";
	     }
	     ...
	     package main;
	     my	$self =	MyClass->new( 'Foozle' )

       Some additional notes about these constructors:

       o   The "Template::*:new" methods allow you to specify a	name for your
	   method other	than "init" by passing the "init_method" parameter:

	     use Class::MakeMethods::Template::Hash (
	       'new --and_then_init' =>	[
		   'new' => { init_method =>  'my_init'	}
	       ],
	     );

       o   If you know that you're not going to	have a complex class
	   hierarchy, you can reduce resource consumption a bit	by changing
	   the above declarations from "*::Hash" to "*::Array" so your objects
	   end up as blessed arrays rather than	blessed	hashes.

   Changing Method Names
       The Template subclasses allow you to control the	names assigned to the
       methods you generate by selecting from several naming interfaces.

       For example, the	accessors declared above use a default,	Perl-ish style
       interface, in which a single method can be called without an argument
       to retrieve the value, or with an argument to set it.  However, you can
       also select a more Java-like syntax, with separate get* and set*
       methods,	by including the '--java' template specification:

	 package MyStruct;
	 use Class::MakeMethods::Template::Hash	(
	   'new'     =>	'new',
	   'scalar'  =>	'--java	Foo',
	 );

       (Note that the declaration of Foo could also have been written as
       'scalar --java' => 'Foo'	or "'scalar' =>	['--java', 'Foo']", or
       "'scalar' => [ 'foo' =" { 'interface'=>'java' } ], all of which are
       interpreted identically;	see the	Class::MakeMethods section on
       "Argument Normalization"	for details.)

       Usage of	this accessor would then be as follows:

	 package main;
	 use MyStruct;

	 my $obj = MyStruct->new( setFoo => "Foozle" );
	 print $obj->getFoo();
	 $obj->setFoo("Bozzle");

   Selecting Specific Helper Methods
       You can use the ability to specify interfaces to	select specific	helper
       methods rather than getting the default collection.

       For example, let's say you wanted to use	a Template::Hash:array,	but
       you only	wanted two methods to be installed in your class, a foo()
       accessor	and a shift_foo() mutator. Any of the below combinations of
       syntax should do	the trick:

	 use Class::MakeMethods::Template::Hash
	   'array' => [
	     'foo' => {	interface=>{'foo'=>'get_set', 'shift_foo'=>'shift'} },
	   ];

       If you're going to have a lot of	methods	with the same interface, you
       could pre-declare a named interface once	and use	it repeatedly:

	 BEGIN {
	   require Class::MakeMethods::Template::Hash;
	   Class::MakeMethods::Template::Hash->named_method('array')->
	       {'interface'}->{'my_get_set_shift'} =
		   { '*'=>'get_set', 'shift_*'=>'shift'	};
	 }

	 use Class::MakeMethods::Template::Hash
	   'array --my_get_set_shift' => [ 'foo', 'bar'	];

   Tree	Structure Example
       In this example we will create a	pair of	classes	with references	to
       other objects.

       The first class is a single-value data object implemented as a
       reference to a scalar.

	 package MyTreeData;
	 use Class::MakeMethods::Template::Scalar (
	   'new'     =>	'new',
	   'string'  =>	'value',
	 );

       The second class	defines	a node in a tree, with a constructor, an
       accessor	for a data object from the class above,	and accessors for a
       list of child nodes.

	 package MyTreeNode;
	 use Class::MakeMethods::Template::Hash	(
	   'new'     =>	'new',
	   'object -class MyTreeData'  => 'data',
	   'array_of_objects -class MyTreeNode'	=> 'children',
	 );

	 sub depth_first_data {
	   my $self = shift;
	   return $self->data, map { $_->depth_first_data() } $self->children;
	 }

       Here's a	sample of how the above	classes	could be used in a program.

	 package main;
	 use MyTreeData;
	 use MyTreeNode;

	 my $node = MyTreeNode->new(
	     data => { value=>'data1' },
	     children => [ { value=>'data3' } ]
	 );
	 $node->push_children( MyTreeNode->new(	data =>	{ value=>'data2' } ) );

	 foreach my $data ( $node->depth_first_data ) {
	   print $data->value();
	 }

SEE ALSO
       See Class::MakeMethods for general information about this distribution.

   Annotated Tutorials
       Ron Savage has posted a pair of annotated examples, linked to below.
       Each demonstrates building a class with MakeMethods, and	each includes
       scads of	comments that walk you through the logic and demonstrate how
       the various methods work	together.

	 http://savage.net.au/Perl-tutorials.html
	 http://savage.net.au/Perl-tutorials/tut-33.tgz
	 http://savage.net.au/Perl-tutorials/tut-34.tgz

perl v5.24.1			  2004-09-06	MakeMethods::Docs::Examples(3)

NAME | EXAMPLES | SEE ALSO

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