Provided by: libclass-makemethods-perl_1.01-5_all bug

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:

       •   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' }
               ],
             );

       •   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