Matthew Simon Cavalletto

NAME

Class::MakeMethods::Emulator::MethodMaker - Emulate Class::MethodMaker

SYNOPSIS

  package MyObject;
  use Class::MakeMethods::Emulator::MethodMaker( 
    new_with_init => 'new',
    get_set       => [ qw / foo bar baz / ];
  );

  ... OR ...

  package MyObject;
  use Class::MakeMethods::Emulator::MethodMaker '-take_namespace';
  use Class::MethodMaker ( 
    new_with_init => 'new',
    get_set       => [ qw / foo bar baz / ];
  );

COMPATIBILITY

This module provides emulation of Class::MethodMaker, using the Class::MakeMethods framework.

Although originally based on Class::MethodMaker, the calling convention for Class::MakeMethods differs in a variety of ways; most notably, the names given to various types of methods have been changed, and the format for specifying method attributes has been standardized. This package uses the aliasing capability provided by Class::MakeMethods, defining methods that modify the declaration arguments as necessary and pass them off to various subclasses of Class::MakeMethods.

There are several ways to call this emulation module:

  • Direct Access

    Replace occurances in your code of Class::MethodMaker with Class::MakeMethods::Emulator::MethodMaker.

  • Install Emulation

    If you use Class::MakeMethods::Emulator::MethodMaker '-take_namespace', the Class::MethodMaker namespace will be aliased to this package, and calls to the original package will be transparently handled by this emulator.

    To remove the emulation aliasing, call use Class::MakeMethods::Emulator::MethodMaker '-release_namespace'.

    Note: This affects all subsequent uses of Class::MethodMaker in your program, including those in other modules, and might cause unexpected effects.

  • The -sugar Option

    Passing '-sugar' as the first argument in a use or import call will cause the 'methods' package to be declared as an alias to this one.

    This allows you to write declarations in the following manner.

      use Class::MakeMethods::Emulator::MethodMaker '-sugar';
    
      make methods
        get_set => [ qw / foo bar baz / ],
        list    => [ qw / a b c / ];

    Note: This feature is deprecated in Class::MethodMaker version 0.96 and later.

DESCRIPTION

NOTE: The documentation below is derived from version 1.02 of Class::MethodMaker, and has been reused with only minor revisions and annotations. Class::MakeMethods::Emulator::MethodMaker provides support for all of the features and examples shown below, with no changes required.

The argument to 'use' is a hash whose keys are the names of types of generic methods defined by MethodMaker and whose values tell MethodMaker what methods to make. More precisely, the keys are the names of MethodMaker methods and the values are the arguments to those methods.

To override any generated methods, it is sufficient to ensure that the overriding method is defined when MethodMaker is called. Note that the use keyword introduces a BEGIN block, so you may need to define (or at least declare) your overriding method in a BEGIN block.

CONSTRUCTOR METHODS

new

Creates a basic constructor.

Takes a single string or a reference to an array of strings as its argument. For each string creates a simple method that creates and returns an object of the appropriate class.

This method may be called as a class method, as usual, or as in instance method, in which case a new object of the same class as the instance will be created. Note that new_hash_init works slightly differently with regard to being called on an instance.

new_with_init

Creates a basic constructor which calls a method named init after instantiating the object. The init method should be defined in the class using MethodMaker.

Takes a single string or a reference to an array of strings as its argument. For each string creates a simple method that creates an object of the appropriate class, calls init on that object propagating all arguments, before returning the object.

This method may be called as a class method, as usual, or as in instance method, in which case a new object of the same class as the instance will be created. Note that new_hash_init works slightly differently with regard to being called on an instance.

new_hash_init

Creates a basic constructor which accepts a hash of slot-name/value pairs with which to initialize the object. The slot-names are interpreted as the names of methods that can be called on the object after it is created and the values are the arguments to be passed to those methods.

Takes a single string or a reference to an array of strings as its argument. For each string creates a method that takes a list of arguments that is treated as a set of key-value pairs, with each such pair causing a call $self->key ($value).

This method may be called as a class method, causing a new instance to be created, or as an instance method, which will operate on the subject instance. This allows it to be combined with new_with_init (see above) to provide some default values. For example, declare a new_with_init method, say 'new' and a new_hash_init method, for example, 'hash_init' and then in the init method, you can call modify or add to the %args hash and then call hash_init.

Note that the operation with regard to action on an instance differs to that of new and new_with_init differently with regard to being called on an instance.

copy (EXPERIMENTAL)

Produce a copy of self. The copy is a *shallow* copy; any references will be shared by the instance upon which the method is called and the returned newborn.

SCALAR ACCESSORS

get_set

Takes a single string or a reference to an array of strings as its argument. Each string specifies a slot, for which accessor methods are created. The accessor methods are, by default:

x

If an argument is provided, sets a new value for x. This is true even if the argument is undef (cf. no argument, which does not set.)

Returns (new) value.

Value defaults to undef.

clear_x

Sets value to undef. This is exactly equivalent to

  $foo->x (undef)

No return.

This is your basic get/set method, and can be used for slots containing any scalar value, including references to non-scalar data. Note, however, that MethodMaker has meta-methods that define more useful sets of methods for slots containing references to lists, hashes, and objects.

Options (EXPERIMENTAL)

There are several options available for controlling the names and types of methods created.

The following options affect the type of methods created:

-static

The methods will refer to a class-specific, rather than instance-specific store. I.e., these scalars are shared across all instances of your object in your process.

The following options affect the methods created as detailed:

-java

Creates getx and setx methods, which return the value, and set the value (no return), respectively.

-eiffel

Creates x and set_x methods, analogous to -java get_x and set_x respectively.

-compatibility

Creates x (as per the default), and clear_x, which resets the slot value to undef. Use this to ensure backward compatibility.

-noclear

Creates x (as per the default) only.

Alternatively, an arrayref specifying an interface for method names may be supplied. Each name must contain a '*' character, which will be replaced by the slot name, and no two patterns may be the same. undef may be supplied for methods that you do not want created. Currently, the first 4 members of such an arrayref may be used:

0

Creates a method that if supplied an argument, sets the slot to the value of that argument; the value of the slot (after setting, if relevant) is returned.

1

Creates a method that takes no arguments, sets the slot value to undefined, and makes no return.

2

Creates a method that takes no arguments, and returns the value of the slot.

3

Creates a method that takes one argument, and sets the value of the slot to that value. Given undef as that argument, the value is set to undef. If called with no arguments, the slot value is set to undef.

See the examples.

Examples

Creates methods a, b, c which can be used for both getting and setting the named slots:

  use Class::MakeMethods::Emulator::MethodMaker
    get_set => 'a',
    get_set => [qw/ b c /];

Creates get_d which returns the value in slot d (takes no arguments), and set_d, which sets the value in slot d (no return):

  use Class::MakeMethods::Emulator::MethodMaker
    get_set => [ -java => d ];

Creates e_clear, e_get, e_set, f_clear, f_get, f_set methods:

  use Class::MakeMethods::Emulator::MethodMaker
    get_set => [[undef, '*_clear', '*_get', '*_set'] => qw/e f/ ];

get_concat

Like get_set except sets do not clear out the original value, but instead concatenate the new value to the existing one. Thus these slots are only good for plain scalars. Also, like get_set, defines clear_foo method.

The argument taken may be a hashref, in which the keys name and join are recognized; name being the slot name, join being a join string t glue any given strings.

Example:

  use Class::MakeMethods::Emulator::MethodMaker
    get_concat => { name => 'words', join => "\t" };

Will, each time an argument is supplied to the x method, glue this argument onto any existing value with tab separator. Like the join operator, the join field is applied between values, not prior to the first or after the last.

counter

Create components containing simple counters that may be read, incremented, or reset. For value x, the methods are:

x

(accepts argument to set),

incr_x

(accepts argument for increment size),

reset_x.

The counter is implicitly initialized to zero.

OBJECT ACCESSORS

object

Creates methods for accessing a slot that contains an object of a given class as well as methods to automatically pass method calls onto the object stored in that slot.

    object => [
               'Foo' => 'phooey',
               'Bar' => [ qw / bar1 bar2 bar3 / ],
               'Baz' => {
                         slot => 'foo',
                         comp_mthds => [ qw / bar baz / ]
                        },
               'Fob' => [
                         {
                          slot => 'dog',
                          comp_mthds => 'bark',
                         },
                         {
                          slot => 'cat',
                          comp_mthds => 'miaow',
                         },
                        ];
              ];

The main argument should be a reference to an array. The array should contain pairs of class => sub-argument pairs. The sub-arguments parsed thus:

Hash Reference

See Baz above. The hash should contain the following keys:

slot

The name of the instance attribute (slot).

comp_mthds

A string or array ref, naming the methods that will be forwarded directly to the object in the slot.

Array Reference

As for String, for each member of the array. Also works if each member is a hash reference (see Fob above).

String

The name of the instance attribute (slot).

For each slot x, with forwarding methods y and z, the following methods are created:

x

A get/set method.

If supplied with an object of an appropriate type, will set set the slot to that value.

Else, if the slot has no value, then an object is created by calling new on the appropriate class, passing in any supplied arguments.

The stored object is then returned.

y

Forwarded onto the object in slot x, which is auto-created via new if necessary. The new, if called, is called without arguments.

z

As for y.

So, using the example above, a method, foo, is created in the class that calls MethodMaker, which can get and set the value of those objects in slot foo, which will generally contain an object of class Baz. Two additional methods are created in the class using MethodMaker, named 'bar' and 'baz' which result in a call to the 'bar' and 'baz' methods on the Baz object stored in slot foo.

object_list

Functions like list, but maintains an array of referenced objects in each slot. Forwarded methods return a list of the results returned by maping the method over each object in the array.

Arguments are like object.

forward

  forward => [ comp => 'method1', comp2 => 'method2' ]

Define pass-through methods for certain fields. The above defines that method method1 will be handled by component comp, whilst method method2 will be handled by component comp2.

REFERENCE ACCESSORS

list

Creates several methods for dealing with slots containing list data. Takes a string or a reference to an array of strings as its argument and for each string, x, creates the methods:

x

This method returns the list of values stored in the slot. In an array context it returns them as an array and in a scalar context as a reference to the array.

x_push
x_pop
x_shift
x_unshift
x_splice
x_clear
x_count

Returns the number of elements in x.

x_index

Takes a list of indices, returns a list of the corresponding values.

x_set

Takes a list, treated as pairs of index => value; each given index is set to the corresponding value. No return.

hash

Creates a group of methods for dealing with hash data stored in a slot.

Takes a string or a reference to an array of strings and for each string, x, creates:

x

Called with no arguments returns the hash stored in the slot, as a hash in a list context or as a reference in a scalar context.

Called with one simple scalar argument it treats the argument as a key and returns the value stored under that key.

Called with one array (list) reference argument, the array elements are considered to be be keys of the hash. x returns the list of values stored under those keys (also known as a hash slice.)

Called with one hash reference argument, the keys and values of the hash are added to the hash.

Called with more than one argument, treats them as a series of key/value pairs and adds them to the hash.

x_keys

Returns the keys of the hash.

x_values

Returns the list of values.

x_tally

Takes a list of arguments and for each scalar in the list increments the value stored in the hash and returns a list of the current (after the increment) values.

x_exists

Takes a single key, returns whether that key exists in the hash.

x_delete

Takes a list, deletes each key from the hash.

x_clear

Resets hash to empty.

tie_hash

Much like hash, but uses a tied hash instead.

Takes a list of pairs, where the first is the name of the component, the second is a hash reference. The hash reference recognizes the following keys:

tie

Required. The name of the class to tie to. Make sure you have used the required class.

args

Required. Additional arguments for the tie, as an array ref.

The first argument can also be an arrayref, specifying multiple components to create.

Example:

   tie_hash     => [
                    hits        => {
                                    tie => qw/ Tie::RefHash /,
                                    args => [],
                                   },
                   ],

hash_of_lists

Creates a group of methods for dealing with list data stored by key in a slot.

Takes a string or a reference to an array of strings and for each string, x, creates:

x

Returns all the values for all the given keys, in order. If no keys are given, returns all the values (in an unspecified key order).

The result is returned as an arrayref in scalar context. This arrayref is not part of the data structure; messing with it will not affect the contents directly (even if a single key was provided as argument.)

If any argument is provided which is an arrayref, then the members of that array are used as keys. Thus, the trivial empty-key case may be utilized with an argument of [].

x_keys

Returns the keys of the hash. As an arrayref in scalar context.

x_exists

Takes a list of keys, and returns whether each key exists in the hash (i.e., the and of whether the individual keys exist).

x_delete

Takes a list, deletes each key from the hash.

x_push

Takes a key, and some values. Pushes the values onto the list denoted by the key. If the first argument is an arrayref, then each element of that arrayref is treated as a key and the elements pushed onto each appropriate list.

x_pop

Takes a list of keys, and pops each one. Returns the list of popped elements. undef is returned in the list for each key that is has an empty list.

x_last

Like x_pop, but does not actually change any of the lists.

x_unshift

Like push, only the from the other end of the lists.

x_shift

Like pop, only the from the other end of the lists.

x_splice

Takes a key, offset, length, and a values list. Splices the list named by the key. Anything from the offset argument (inclusive) may be omitted. See "splice" in perlfunc.

x_set

Takes a key, and a set of index->value pairs, and sets each specified index to the corresponding value for the given key.

x_clear

Takes a list of keys. Resets each named list to empty (but does not delete the keys.)

x_count

Takes a list of keys. Returns the sum of the number of elements for each named list.

x_index

Takes a key, and a list of indices. Returns a list of each item at the corresponding index in the list of the given key. Uses undef for indices beyond range.

x_remove

Takes a key, and a list of indices. Removes each corresponding item from the named list. The indices are effectively looked up at the point of call -- thus removing indices 3, 1 from list (a, b, c, d) will remove (d) and (b).

x_sift

Takes a key, and a set of named arguments, which may be a list or a hash ref. Removes list members based on a grep-like approach.

filter

The filter function used (as a coderef). Is passed two arguments, the value compared against, and the value in the list that is potential for grepping out. If returns true, the value is removed. Default:

  sub { $_[0] == $_[1] }
keys

The list keys to sift through (as an arrayref). Unknown keys are ignored. Default: all the known keys.

values

The values to sift out (as an arrayref). Default: [undef]

Options:

-static

Make the corresponding storage class-specific, rather than instance-specific.

STATIC ACCESSORS

static_get_set

Like get_set, takes a single string or a reference to an array of strings as its argument. For each string, x creates two methods:

x

If an argument is provided, sets a new value for x. Returns (new) value. Value defaults to undef.

clear_x

Sets value to undef. No return.

The difference between this and get_set is that these scalars are shared across all instances of your object in your process.

static_hash

Much like hash, but uses a class-based hash instead.

GROUPED ACCESSORS

boolean

  boolean => [ qw / foo bar baz / ]

Creates methods for setting, checking and clearing flags. All flags created with this meta-method are stored in a single vector for space efficiency. The argument to boolean should be a string or a reference to an array of strings. For each string x it defines several methods:

x

Returns the value of the x-flag. If called with an argument, it first sets the x-flag to the truth-value of the argument.

set_x

Equivalent to x(1).

clear_x

Equivalent to x(0).

Additionally, boolean defines three class methods:

bits

Returns the vector containing all of the bit fields (remember however that a vector containing all 0 bits is still true).

boolean_fields

Returns a list of all the flags by name.

bit_dump

Returns a hash of the flag-name/flag-value pairs.

grouped_fields

Creates get/set methods like get_set but also defines a method which returns a list of the slots in the group.

  use Class::MakeMethods::Emulator::MethodMaker
    grouped_fields => [
      some_group => [ qw / field1 field2 field3 / ],
    ];

Its argument list is parsed as a hash of group-name => field-list pairs. Get-set methods are defined for all the fields and a method with the name of the group is defined which returns the list of fields in the group.

struct

  struct => [  qw / foo bar baz / ];

Creates methods for setting, checking and clearing values which are stored by position in an array. All the slots created with this meta-method are stored in a single array.

The argument to struct should be a string or a reference to an array of strings. For each string meta-method x, it defines two methods: x and clear_x. x returns the value of the x-slot. If called with an argument, it first sets the x-slot to the argument. clear_x sets the slot to undef.

Additionally, struct defines three class method: struct, which returns a list of all of the struct values, struct_fields, which returns a list of all the slots by name, and struct_dump, which returns a hash of the slot-name/slot-value pairs.

Note: This feature is included but not documented in Class::MethodMaker version 1.

INDEXED ACCESSORS

listed_attrib

  listed_attrib => [ qw / foo bar baz / ]

Like boolean, listed_attrib creates x, set_x, and clear_x methods. However, it also defines a class method x_objects which returns a list of the objects which presently have the x-flag set to true. N.B. listed_attrib does not use the same space efficient implementation as boolean, so boolean should be prefered unless the x_objects method is actually needed.

key_attrib

  key_attrib => [ qw / foo bar baz / ]

Creates get/set methods like get/set but also maintains a hash in which each object is stored under the value of the field when the slot is set. If an object has a slot set to a value which another object is already set to the object currently set to that value has that slot set to undef and the new object will be put into the hash under that value. (I.e. only one object can have a given key. The method find_x is defined which if called with any arguments returns a list of the objects stored under those values in the hash. Called with no arguments, it returns a reference to the hash.

key_with_create

  key_with_create => [ qw / foo bar baz / ]

Just like key_attrib except the find_x method is defined to call the new method to create an object if there is no object already stored under any of the keys you give as arguments.

CODE ACCESSORS

code

  code => [ qw / foo bar baz / ]

Creates a slot that holds a code reference. Takes a string or a reference to a list of string and for each string, x, creates a method x which if called with one argument which is a CODE reference, it installs that code in the slot. Otherwise it runs the code stored in the slot with whatever arguments (including none) were passed in.

method

  method => [ qw / foo bar baz / ]

Just like code, except the code is called like a method, with $self as its first argument. Basically, you are creating a method which can be different for each object. Which is sort of weird. But perhaps useful.

abstract

  abstract => [ qw / foo bar baz / ]

This creates a number of methods will die if called. This is intended to support the use of abstract methods, that must be overidden in a useful subclass.

ARRAY CONSTRUCTOR AND ACCESSORS

builtin_class (EXPERIMENTAL)

Purpose: This class generates a wrapper around some builtin function, cacheing the results in the object and providing a by-name interface.

Takes a (core) function name, and a arrayref of return position names (we will call it pos_list). Creates:

new

Calls the core func with any given arguments, stores the result in the instance.

x

For each member of pos_list, creates a method of the same name which gets/sets the nth member of the returned list, where n is the position of x in pos_list.

fields

Returns pos_list, in the given order.

dump

Returns a list item name, item value, in order.

Example Usage:

  package Stat;

  use Class::MakeMethods::Emulator::MethodMaker
    builtin_class => [stat => [qw/ dev ino mode nlink /]],

  package main;

  my $file = "$ENV{HOME}/.profile";
  my $s = Stat->new ($file);
  print "File $file has ", $s->nlink, " links\n";

Note that (a) the new method does not check the return value of the function called (in the above example, if $file does not exist, you will silently get an empty object), and (b) if you really want the above example, see the core File::stat module. But you get the idea, I hope.

CONVERSION

If you wish to convert your code from use of the Class::MethodMaker emulator to direct use of Class::MakeMethods, you will need to adjust the arguments specified in your use or make calls.

Often this is simply a matter of replacing the names of aliased method-types listed below with the new equivalents.

For example, suppose that you code contained the following declaration:

  use Class::MethodMaker ( 
    counter => [ 'foo' ]
  );

Consulting the listings below you can find that counter is an alias for Hash:number --counter and you could thus revise your declaration to read:

  use Class::MakeMethods ( 
    'Hash:number --counter' => [ 'foo' ] 
  );

However, note that those methods marked "(with custom interface)" below have a different default naming convention for helper methods in Class::MakeMethods, and you will need to either supply a similar interface or alter your module's calling interface.

Also note that the forward, object, and object_list method types, marked "(with modified arguments)" below, require their arguments to be specified differently.

See Class::MakeMethods::Template::Generic for more information about the default interfaces of these method types.

Hash methods

The following equivalencies are declared for old meta-method names that are now handled by the Hash implementation:

  new              'Template::Hash:new --with_values'
  new_with_init    'Template::Hash:new --with_init'
  new_hash_init    'Template::Hash:new --instance_with_methods'
  copy             'Template::Hash:copy'
  get_set          'Template::Hash:scalar' (with custom interfaces)
  counter          'Template::Hash:number --counter'
  get_concat       'Template::Hash:string --get_concat' (with custom interface)
  boolean          'Template::Hash:bits' (with custom interface)
  list             'Template::Hash:array' (with custom interface)
  struct           'Template::Hash:struct'
  hash             'Template::Hash:hash' (with custom interface)
  tie_hash         'Template::Hash:tiedhash' (with custom interface)
  hash_of_lists    'Template::Hash:hash_of_arrays'
  code             'Template::Hash:code'
  method           'Template::Hash:code --method'
  object           'Template::Hash:object' (with custom interface and modified arguments)
  object_list      'Template::Hash:array_of_objects' (with custom interface and modified arguments)
  key_attrib       'Template::Hash:string_index'
  key_with_create  'Template::Hash:string_index --find_or_new'

Static methods

The following equivalencies are declared for old meta-method names that are now handled by the Static implementation:

  static_get_set   'Template::Static:scalar' (with custom interface)
  static_hash      'Template::Static:hash' (with custom interface)

Flyweight method

The following equivalency is declared for the one old meta-method name that us now handled by the Flyweight implementation:

  listed_attrib   'Template::Flyweight:boolean_index'

Struct methods

The following equivalencies are declared for old meta-method names that are now handled by the Struct implementation:

  builtin_class   'Template::Struct:builtin_isa'

Universal methods

The following equivalencies are declared for old meta-method names that are now handled by the Universal implementation:

  abstract         'Template::Universal:croak --abstract'
  forward          'Template::Universal:forward_methods' (with modified arguments)

EXTENDING

In order to enable third-party subclasses of MethodMaker to run under this emulator, several aliases or stub replacements are provided for internal Class::MethodMaker methods which have been eliminated or renamed.

  • install_methods - now simply return the desired methods

  • find_target_class - now passed in as the target_class attribute

  • ima_method_maker - no longer supported; use target_class instead

BUGS

This module aims to provide a 100% compatible drop-in replacement for Class::MethodMaker; if you detect a difference when using this emulation, please inform the author.

There are no known incompatibilities at this time.

The test suite from Class::MethodMaker version 1.02 is included with this package. The tests are unchanged except for the a direct substitution of Class::MakeMethods::Emulator::MethodMaker in the place of Class::MethodMaker.

Earlier Versions

In cases where Class::MethodMaker version 0.92's test suite contained a different version of a test, it is also included. (Note that version 0.92's get_concat returned '' for empty values, but in version 0.96 this was changed to undef; this emulator follows the later behavior. To avoid "use of undefined value" warnings from the 0.92 version of get_concat.t, that test has been modified by appending a new flag after the name, 'get_concat --noundef', which restores the earlier behavior.)

SEE ALSO

See Class::MethodMaker for more information about the original module.

A good introduction to Class::MethodMaker is provided by pages 222-234 of Object Oriented Perl, by Damian Conway (Manning, 1999).

  http://www.browsebooks.com/Conway/ 

The following tutorials provide usage examples and accompanying commentary for Class::MethodMaker:

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

See Class::MakeMethods for an overview of the method-generation framework this is based on.

See Class::MakeMethods::Guide for a getting-started guide, annotated examples of usage, and a listing of the method generation classes included in this distribution.

See Class::MakeMethods::ReadMe for distribution, installation, version and support information.

AUTHORS

Developed by:

  M. Simon Cavalletto, Evolution Online Systems, simonm@evolution.com

Based on Class::MethodMaker, originally developed by:

  Peter Seibel, Organic Online

Class::MethodMaker is currently maintained by:

  Martyn J. Pearce

LICENSE

This module is free software. It may be used, redistributed and/or modified under the same terms as Perl.

Copyright (c) 1998, 1999, 2000, 2001 Evolution Online Systems, Inc.

Portions Copyright (c) 1996 Organic Online

Portions Copyright (c) 2000 Martyn J. Pearce.

3 POD Errors

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