NAME

Object::Simple::Guides - Object::Simple Guides

GUIDES

1. Generate accessor

At first, you create a class extending Object::Simple to use methods of Object::Simple.

    package SomeClass;
    
    use base 'Object::Simple';

Object::Simple have new() method. This is a constructor. It can receive hash and hash reference as arguments.

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

You can generate accessor by attr() method.

    __PACKAGE__->attr('foo');

You can set and get the value by accessor.

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

You can specify a default value for the accessor.

    __PACKAGE__->attr(foo => 1);

If the value of foo is not exists and foo() is called, You can get the default value.

    my $default_value = $obj->foo;

If you want to specify a reference or object as default value, it must be sub reference, whose return value is the default value. This is requirment not to share the default value with other objects.

    __PACKAGE__->attr(foo => sub { [] });
    __PACKAGE__->attr(foo => sub { {} });
    __PACKAGE__->attr(foo => sub { SomeClass->new });

You can generate accessors at once.

    __PACKAGE__->attr([qw/foo bar baz/]);
    __PACKAGE__->attr([qw/foo bar baz/] => 0);

Example:

I show a example to understand Object::Simple well.

Point class, which have two attribute, x and y, and clear() method to set x and y to 0.

    package Point;
    
    use strict;
    use warnings;
    
    use base 'Object::Simple';

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

Point3D class, which inherit Point class. This class has z attribute in addition to x and y. clear() method is overridden to clear x, y and z.

    package Point3D;
    
    use strict;
    use warnings;
    
    use base 'Point';
    
    __PACKAGE__->attr(z => 0);
    
    sub clear {
        my $self = shift;
        
        $self->SUPER::clear();
        
        $self->z(0);
    }

2. Concepts of Object-Oriented programing

Inheritance

I explain the essence of Object-Oriented programing to use Object::Simple well.

First concept of Object-Oriented programing is Inheritance. Inheritance means that If Class Q inherit Class P, Class Q can call all method of class P.

    +---+
    | P | Base class
    +---+   having method1() and method2()
      |
    +---+
    | Q | Sub class
    +---+   having method3()

Class Q inherits Class P, so Q can call all methods of P in addition to methods of Q. In other words, Q can call method1(), method2(), and method3()

To inherit a class, use base module.

    package P;
    
    sub method1 { ... }
    sub method2 { ... }
    
    package Q;
    
    use base 'P';
    
    sub method3 { ... }

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

To know the object is belong to what class, use ref() function.

    my $class = ref $obj;

To know whether the object inherits the specified class, use isa() method.

    $obj->isa('SomeClass');

To know whether the object(or class) can call the specified method, use can() method

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

Capsulation

Second concept of Object-Oriented programing is capsulation. Capsulation means that you don't touch internal data directory. You must use public methods in documentation. If you keep this rule, All the things become simple.

To keep this rule, Use accessor to get and set to the value.

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

To access the value directory is bad manner.

    my $value = $obj->{foo}; # Bad manner!
    $obj->{foo} = 1;         # Bad manner!

Polymorphism

Third concept Object-Oriented programing is polymorphism. Polymorphism is devieded into two concepts, overloading and overriding.

Perl programer don't have to care overloading. Perl is dynamic language, so subroutine can receive any value. Overloading is worth for languages having static type variable, like C++ or Java.

Overriding means that in sub class you can change the process of the base class's method.

    package P;
    
    sub method1 { return 1 }
    
    package Q;
    
    use base 'P';
    
    sub method1 { return 2 }

method1() of class P return 1. method1() of class Q return 2. That is to say, method1() is overridden in class Q.

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

If you want to call the method of base class from sub class, use SUPER pseudo-class.

    package Q;
    
    sub method1 {
        my $self = shift;
        
        my $value = $self->SUPER::method1(); # return value is 1
        
        return 2 + $value;
    }

If you understand only these three concepts, you can do enough powerful Object-Oriented programming. and source code is readable for other language users.

3. Offten used techniques

Override new() method

new() method is overridden if needed.

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 by overridden new() method.

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

4. Other features

Strict arguments check

Object::Simple pay attention to the usability. If wrong number arguments is passed to new() method, exception is thrown.

    my $obj = SomeClass->new(1); # Exception!

as is the accessor.

    $obj->foo(a => 1); # Execption!

Import methods

You can import methods of Object::Simple. This is useful in case you don't want to use multiple inheritance.

    package SomeClass;
    
    use Object::Simple qw/new attr/;
    
    __PACKAGE__->attr('foo');

Note that you can't override new() method because new() method is imported in the class, not inherited from base class.

Method chain

Method chain is available because accessor return self-object when it is called to set the value,

    $obj->foo(1)->bar(4)->baz(6);

STABILITY

Object::Simple is stable. APIs and the implementations will not be changed in the future.

DEPRECATED

class_attr and dual_attr is deprecated because this is not good practice in Object Oriented programming. To know the usages, see old documentation before 3.0612.

cpanm Object::Simple

perl -MCPAN -e shell
install Object::Simple