The Perl Toolchain Summit needs more sponsors. If your company depends on Perl, please support this very important event.
 / 
Object-Simple-3.16
River stage two • 6 direct dependents • 14 total dependents
10 ++
/ Object::Simple

NAME

Object::Simple - Simple class builder(Mojo::Base porting)

SYNOPSIS

  package SomeClass;
  use Object::Simple -base;
  
  # Create accessor
  has 'foo';
  
  # Create accessor with default value
  has foo => 1;
  has foo => sub { [] };
  has foo => sub { {} };
  has foo => sub { OtherClass->new };
  
  # Create accessors at once
  has [qw/foo bar baz/];
  has [qw/foo bar baz/] => 0;

Create object.

  # Create a new object
  my $obj = SomeClass->new;
  my $obj = SomeClass->new(foo => 1, bar => 2);
  my $obj = SomeClass->new({foo => 1, bar => 2});
  
  # Set and get value
  my $foo = $obj->foo;
  $obj->foo(1);
  
  # set-accessor can be changed
  $obj->foo(1)->bar(2);

Inheritance

  # Foo.pm
  package Foo;
  use Object::Simple -base;
  
  # Bar.pm
  package Bar;
  use Foo -base;
  
  # Bar.pm (another way to inherit)
  package Bar;
  use Object::Simple -base => 'Foo';

DESCRIPTION

Object::Simple is Mojo::Base porting. you can use Mojo::Base features.

Object::Simple is a generator of accessor method, such as Class::Accessor, Mojo::Base, or Moose.

Class::Accessor is simple, but lack offten used features. new method can't receive hash arguments. Default value can't be specified. If multipule values is set through the accessor, its value is converted to array reference without warnings.

Some people find Moose too complex, and dislike that it depends on outside modules. Some say that Moose is almost like another language and does not fit the familiar perl syntax. In some cases, in particular smaller projects, some people feel that Moose will increase complexity and therefore decrease programmer efficiency. In addition, Moose can be slow at compile-time and its memory usage can get large.

Object::Simple is the middle way between Class::Accessor and complex class builder. Only offten used features is implemented has no dependency. Object::Simple is almost same as Mojo::Base.

new method can receive hash or hash reference. You can specify default value.

If you like Mojo::Base, Object::Simple is good choice.

GUIDE

1. Create accessor

At first, you create class.

  package SomeClass;
  use Object::Simple -base;

By using -base option, SomeClass inherit Object::Simple and import has method.

Object::Simple have new method. new method is constructor. new method can receive hash or hash reference.

  my $obj = SomeClass->new;
  my $obj = SomeClass->new(foo => 1, bar => 2);
  my $obj = SomeClass->new({foo => 1, bar => 2});

Create accessor by using has function.

  has 'foo';

If you create accessor, you can set or get attribute value.s

  # Set value
  $obj->foo(1);
  
  # Get value
  my $foo = $obj->foo;

set-accessor can be changed.

  $obj->foo(1)->bar(2);

You can define default value.

  has foo => 1;

If foo attribute value is not exists, default value is used.

  my $foo_default = $obj->foo;

If you want to use reference or object as default value, default value must be surrounded by code reference. the return value become default value.

  has foo => sub { [] };
  has foo => sub { {} };
  has foo => sub { SomeClass->new };

You can create multiple accessors at once.

  has [qw/foo bar baz/];
  has [qw/foo bar baz/] => 0;

Class example

I introduce Object::Simple example.

Point class: two accessor x and y, and clear method to set x and y to 0.

  package Point;
  use Object::Simple -base;

  has x => 0;
  has y => 0;
  
  sub clear {
    my $self = shift;
    
    $self->x(0);
    $self->y(0);
  }

Use Point class.

  use Point;
  my $point = Point->new(x => 3, y => 5);
  print $point->x;
  $point->y(9);
  $point->clear;

Point3D class: Point3D inherit Point class. Point3D class has z accessor in addition to x and y. clear method is overriden to clear x, y and z.

  package Point3D;
  use Point -base;
  
  has z => 0;
  
  sub clear {
    my $self = shift;
    
    $self->SUPER::clear;
    
    $self->z(0);
  }

Use Point3D class.

  use Point3D;
  my $point = Point->new(x => 3, y => 5, z => 8);
  print $point->z;
  $point->z(9);
  $point->clear;

2. Concepts of Object-Oriented programing

I introduce concepts of Object-Oriented programing

Inheritance

I explain the essence of Object-Oriented programing.

First concept is inheritance. Inheritance means that if Class Q inherit Class P, Class Q use all methods of class P.

  +---+
  | P | Base class
  +---+   have method1 and method2
    |
  +---+
  | Q | Sub class
  +---+   have method3

Class Q inherits Class P, Q can use all methods of P in addition to methods of Q.

In other words, Q can use method1, method2, and method3

You can use -base option to inherit class.

  # P.pm
  package P;
  use Object::Simple -base;
  
  sub method1 { ... }
  sub method2 { ... }
  
  # Q.pm
  package Q;
  use P -base;
  
  sub method3 { ... }

Perl have useful functions and methods to help Object-Oriented programing.

If you know what class the object is belonged to, use ref function.

  my $class = ref $obj;

If you know what class the object inherits, use isa method.

  $obj->isa('SomeClass');

If you know what method the object(or class) can use, use can method

  SomeClass->can('method1');
  $obj->can('method1');

Encapsulation

Second concept is encapsulation. Encapsulation means that you don't touch internal data directory. You must use public method when you access internal data.

Create accessor and use it to keep thie rule.

  my $value = $obj->foo;
  $obj->foo(1);

Polymorphism

Third concept is polymorphism. Polymorphism is divided into two concepts, overload and override

Perl programer don't need to care overload. Perl is dynamic type language. Subroutine can receive any value.

Override means that you can change method behavior in sub class.

  # P.pm
  package P;
  use Object::Simple -base;
  
  sub method1 { return 1 }
  
  # Q.pm
  package Q;
  use P -base;
  
  sub method1 { return 2 }

P method1 return 1. Q method1 return 2. Q method1 override P method1.

  # P method1 return 1
  my $obj_a = P->new;
  $obj_p->method1; 
  
  # Q method1 return 2
  my $obj_b = Q->new;
  $obj_q->method1;

If you want to use super class method from sub class, use SUPER pseudo-class.

  package Q;
  
  sub method1 {
    my $self = shift;
    
    # Call supper class P method1
    my $value = $self->SUPER::method1;
    
    return 2 + $value;
  }

If you understand three concepts, you have learned Object-Oriented programming primary parts.

3. Often used techniques

Override new method

new method can be overridden.

Example:

Initialize the object

  sub new {
    my $self = shift->SUPER::new(@_);
    
    # Initialization
    
    return $self;
  }

Example:

Change arguments of new.

  sub new {
    my $self = shift;
    
    $self->SUPER::new(x => $_[0], y => $_[1]);
    
    return $self;
  }

You can pass array to new method.

  my $point = Point->new(4, 5);

IMPORT OPTIONS

-base

By using -base option, the class inherit Object::Simple and import has function.

  package Foo;
  use Object::Simple -base;
  
  has x => 1;
  has y => 2;

strict and warnings is automatically enabled.

You can also use -base option in sub class to inherit other class.

  # Bar inherit Foo
  package Bar;
  use Foo -base;

You can also use the following syntax.

  # Same as above
  package Bar;
  use Object::Simple -base => 'Foo';

FUNCTIONS

has

Create accessor.

  has 'foo';
  has [qw/foo bar baz/];
  has foo => 1;
  has foo => sub { {} };

Create accessor. has receive accessor name and default value. Default value is optional. If you want to create multipule accessors at once, specify accessor names as array reference at first argument.

If you want to specify reference or object as default value, it must be code reference not to share the value with other objects.

Get and set a attribute value.

  my $foo = $obj->foo;
  $obj->foo(1);

If a default value is specified and the value is not exists, you can get default value.

If a value is set, the accessor return self object. So you can set a value repeatedly.

  $obj->foo(1)->bar(2);

You can create all accessors at once.

  has [qw/foo bar baz/];

METHODS

new

  my $obj = Object::Simple->new(foo => 1, bar => 2);
  my $obj = Object::Simple->new({foo => 1, bar => 2});

Create a new object. new receive hash or hash reference as arguments.

attr

  __PACKAGE__->attr('foo');
  __PACKAGE__->attr([qw/foo bar baz/]);
  __PACKAGE__->attr(foo => 1);
  __PACKAGE__->attr(foo => sub { {} });

  __PACKAGE__->attr([qw/foo bar baz/]);

Create accessor. attr method usage is equal to has method.

DEPRECATED FUNCTIONALITY

  function exporting of C<new> and C<attr> method # Will be removed 2021/6/1
  
  The syntax of multiple key-value arguments 
    has x => 1, y => 2;      
    __PACAKGE__->attr(x => 1, y => 2);
  # Will be removed 2021/6/1
  
  class_attr method # will be removed 2017/1/1
  dual_attr method # will be removed 2017/1/1

BACKWARDS COMPATIBILITY POLICY

If a functionality is DEPRECATED, you can know it by DEPRECATED warnings. You can check all DEPRECATED functionalities by document. DEPRECATED functionality is removed after five years, but if at least one person use the functionality and tell me that thing I extend one year each time he tell me it.

EXPERIMENTAL functionality will be changed without warnings.

(This policy was changed at 2011/10/22)

BUGS

Tell me the bugs by mail or github http://github.com/yuki-kimoto/Object-Simple

AUTHOR

Yuki Kimoto, <kimoto.yuki at gmail.com>

COPYRIGHT & LICENSE

Copyright 2008-2016 Yuki Kimoto, all rights reserved.

This program is free software; you can redistribute it and/or modify it under the same terms as Artistic v2(This is same as Mojolicious licence).