Milan Adamovsky > OOP-1.01 > OOP

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NAME ^

OOP - Object Oriented Programming Class

SYNOPSIS ^

  # Illustrates how to define a prototype, how the
  # parameters are passed, and how to access the
  # processed parameters.

  use OOP;

  # These are the parameters normally passed 
  # to a class using OOP.pm.
   
  my $classPrototype = {
             one => 1,
             two => 2,
             three => {
                        hi => {
                               dataType => 'hash',
                               allowEmpty => 0,
                               maxLength => 3,
                               minLength => 1,
                               readAccess => 1,
                               required => 1,
                               value => {
                                         bye => '',
                                         ebye => {
                                                  dataType => 'scalar',
                                                  allowEmpty => 0,
                                                  maxLength => 8,
                                                  minLength => 1,
                                                  readAccess => 0,     
                                                  required => 0,
                                                  value => '',
                                                  writeAccess => 1
                                                 }
                                        },
                               writeAccess => 1                                      
                              }
                       }
              };
 
  # These are the parameters normally passed 
  # to a class using OOP.pm.
   
  my $objectProperties = {
                          one => 1,
                          two => 2,
                          three => {
                                    hi => {
                                           bye => '12345678'
                                          }
                                   }
                         };      
             
  my $obj = OOP->new({
                      ARGS=> $objectProperties,
                      PROTOTYPE => $classPrototype
                     });
                   

  print $obj->{PROPERTIES}->{three}{hi}{bye} . "\n";
  print $obj->getProperty($obj->{PROPERTIES}->{three}{hi}{bye}) . "\n";

ABSTRACT ^

This class is intended to complement Object Oriented Programming ("OOP") development by offering solutions to common problems in the OOP world. If not problems then this class will also attempt to facilitate various OOP related tasks and ensure that various conventions are followed, where possible. It provides a developer with various methods that enforce uniform OOP conventions and ensure sound OOP development in PERL.

Simply stated, this class attempts to take out as much of the OOP overhead for the developer as possible while at the same time allowing a developer to write more robust applications.

DESCRIPTION ^

The OOP class allows a developer to restrict property accessbility in more ways than one. The developer can specify anything from how the data should be encapsulated to how many elements can be create dynamically to whether or not the property is read-only, and more...

The approach used in this class to handled properties relies on PERL's tie() function. It is a very useful though often misunderstood and underused feature. Don't worry because this class takes care of everything for the developer; thus, not even a fundamental understanding of tie() is necessary. The code is readily available to those who desire to understand what is happening, but again it is not necessary to do so to use this class.

PROPERTIES

The class takes a slightly more unconventional approach on how properties are handled. The reason for this is to provide greater flexibility and expandibility for future releases of the OOP class. As a matter of fact the chosen approach is one that everyone can understand.

There are three types of properties when using this class. The naming conventions are proprietary to this class and have no relation to any outside terminology that might overlap. Let's go over these properties.

System Attributes

The first type of properties are those passed to the constructor of the OOP class. For sake of concept separation we will refer to these as attributes. These are properties that are more or less static and required for the class to know how it is to operate and what it is to operate on. If this doesn't make sense, simply know that these are required.

These attributes are set when the class is instantiated (or called), as such:

  my $obj = OOP->new({
                      ARGS=> $objectProperties,
                      PROTOTYPE => $classPrototype,
                      CUSTOM => {}
                     });

The argument is an anonymous hash where the keys are the system attributes. If this doesn't make sense to you, simply know to follow the convention above and include the parenthesis and curly brackets as shown above.

The corresponding values are hash references. Do not worry about these for right now as it would take away from our focus. Let's keep our focus on the attributes themselves.

Presently there are the following system attributes (in alphabetical order):

ARGS

This property contains all the properties passed to the constructor of the class ("user class") that uses the OOP class ("OOP class"). An example further down in this document will illustrate this better.

CUSTOM

This property doesn't exist but is a place holder for future development. Due to the strict nature of this class, it is intended to provide a point of entry (or exit) in the event a user would choose to customize the class.

PROTOTYPE

This property contains all the properties and their definitions. Collectively this represents the "prototype" for the constructor of the user class.

The prototype is, in effect, the design of how the properties are to be handled by the OOP class (and consequently the user class).

These attributes happen to be the other two types of properties. It is important to remember that unless otherwise specified all system attributes are required. All system attributes are reserved meaning that a developer should never clutter the namespace by adding custom keys as they could override future developments causing for undesirable side-effects. For this purpose use the CUSTOM system attribute as a safe attribute to funnel your custom data through.

Prototype Properties

This is possibly one of the coolest features of the OOP class. It permits the developer to define accessibility to properties in more ways than just either hiding the information or not (encapsulation). As a matter of fact it allows to control properties to an unprecendented level allowing the developer to control how much or how little access to a property a user class should have.

The prototype is built by way of a hash that is passed to the constructor of the OOP class via the system attributes (see above), as such:

  my $obj = OOP->new({
                      ARGS=> $objectProperties,
                      PROTOTYPE => {
                                    one => {
                                            dataType => 'hash',
                                            allowEmpty => 0,
                                            maxLength => 3,
                                            minLength => 1,
                                            readAccess => 1,
                                            required => 1,
                                            value => {
                                                      abye => '',
                                                      bbye => {...}
                                                     },
                                            writeAccess => 1                                      
                                           },
                                   two => 'foobar',
                                   three => [1,2,3,4]
                                  },
                      CUSTOM => {}
                     });

Attention should be given to the PROTOTYPE attribute in the above illustration where we can see an example of how the prototype properties are implemented.

The above illustrates how to define the various restrictions to a particular property. Keep in mind that this is only the prototype so it does not directly deal with data passed into a constructor. One way of seeing it is as a template that is overlayed with the actual data from the constructor.

Providing a definition of a property is always optional. If none is provided then various logical defaults apply. If one does not provide definitions then it will be considered that the elements (or properties) in the prototype are not exclusive but they are required. In other words one could add properties dynamically but the constructor of the user class would need to have at the very least the properties of the prototype passed to it.

The OOP class guesses that it is a property definition by finding the keyword dataType which happens to be the only reserved keyword (for a hash key). This means that when a user class uses the OOP class it should try to avoid using a parameter called "dataType" as it will trigger the OOP class to process it as a parameter definition and subsequently process all other keys within that level of the hash as prototype properties.

Any other keywords in a property definition each have their own special effects. All of them are required as of this writing but could change in the future. The one property worthy pointing out right now is value.

The value property simply states that if this is the actual value associated with the parameter of whose definition we are in. Thus, in the above example value would be the value of the property one.

To expand on this example, if the property two had a definition then 'foobar' would be shifted to value, as such:

  my $obj = OOP->new({
                      ARGS=> $objectProperties,
                      PROTOTYPE => {
                                    one => {
                                            abye => '',
                                            bbye => {...}
                                           },
                                    two => {
                                            dataType => 'scalar',
                                            allowEmpty => 0,
                                            maxLength => 7,
                                            minLength => 1,
                                            readAccess => 1,
                                            required => 1,
                                            value => 'foobar',
                                            writeAccess => 1                                      
                                           },
                                    three => [1,2,3,4]
                                   },
                       CUSTOM => {}
                     });

In the above example we also see how value of one is the actual value when no definition is provided.

The various properties are explained (in alphabetical order):

allowEmpty

This is a boolean (0 or 1) that simply defines whether or not the value of this parameter is allowed to be empty. If it is set to zero then there must be a value, otherwise a 1 would instruct that the value can be empty.

dataType

This is a literal string containing the type of data found in this parameter. The possible values presently are : hash and scalar. Others should work too, they just have not been tested.

locked

Boolean that takes 1 or 0 to define whether or not the particular property may be removed. If it is set to 1 then it may not be removed otherwise if it set to 0 (zero) then a delete() attempt will succeed.

maxLength

This is a number that indicates several things depending on context. The context is determined by the value of dataType. The table below illustrates the effects based on the corresponding dataType.

'array'

Specifies the maximum possible elements in the array structure. This is not yet supported or enforced as of this writing.

'hash'

Specifies the maximum possible elements in the hash structure. This is enforced both when the hash is passed as a parameter to the constructor as well as when an element is attempted to be added dynamically at runtime.

'scalar'

In the event of a scalar it enforces the maximum length of the scalar.

minLength

This is a number that indicates several things depending on context. The context is determined by the value of dataType. This has the inverse effect of maxLength so see the description of maxLength for an idea of how this property works.

readAccess

A boolean that takes either a 1 or a 0 as a value. This determines whether a user can directly access/read the data in the property. If it is set to '1' then the user can access it directly by specifying the data structure (property). If it is set to '0' however then an accessor needs to be used to access the property safely.

required

A boolean that takes either a 1 or a 0 as a value. Specifies whether or not this property is required or optional. If a property definition is not given to a particular property then it is assumed that the element in the prototype is always required. This gives the developer the ability to override that behavior by setting it to 0 (zero).

When this property is set to zero it means that the value is not required but IF it exists and if a property definition exists (which it does in this case), then enforce the definition as well - even if the element is created dynamically.

A value of 1 indicates that this property must be passed to the constructor.

value

This is the actual value of the property. Normally this is left empty unless it contains further data structures such as hashes, array, etc... In the event of a scalar however, it would indicate the default value and by combining the writeAccess property it could be used as a read-only constant value within the user class. See Prototype Properties for more information on value.

writeAccess

A boolean that takes either a 1 or a 0 as a value. This determines whether a user can dynamically write to the data in the property. If it is set to '1' then the user can write and thus overwrite it by specifying a new value. If it is set to '0' however then this property becomes a read-only property.

Additionally, if this is set to '0' and the dataType is a hash or an array, then it declares that elements may not be created on-the-fly or by passing non-defined elements to the constructor (elements that were not defined in the prototype). Likewise if it is set to '1', then the opposite holds true.

Object Properties

As stated several times throughout this document the OOP class is generally going to be used in a "user class". In the context of this document a "user class" is quite simply a class that uses this OOP class.

Knowing this the next question is 'how do we tie everything together?' Good question! This section will cover just that.

Let's say we are designing a new class called Foo and we want to ensure that when another developer uses our class that all properties that are passed, used and modified are handled according to our prototype (our design).

The very first thing that we need to do is design the properties for a given module by specifying the prototype (see System Attributes and Prototype Properties for more details). We will continue with the assumption that we have a prototype in place.

The next step is to connect this prototype with our user class Foo. We will do so by instantiating the OOP class from within Foo's constructor. This is achieved in a similar fashion:

  package Foo;

  use OOP;

  sub new {

   my ($class, $objectProperties) = (@_);
 
   my $self = bless {}, $class;
 
   my $obj = OOP->new({
                       ARGS=> $objectProperties,
                       PROTOTYPE => {
                                     one => {
                                             dataType => 'hash',
                                             allowEmpty => 0,
                                             maxLength => 3,
                                             minLength => 1,
                                             readAccess => 1,
                                             required => 1,
                                             value => {
                                                       abye => '',
                                                       bbye => {...}
                                                      },
                                             writeAccess => 1                                      
                                            },
                                     two => 'foobar',
                                     three => [1,2,3,4]
                                    }
                      });
   
   $self->{OOP} = $obj;                         # optional but advised
   $self->{myProperties} = $obj->{PROPERTIES};  
   
   return ($self);
   
  }
  
  ...
  
  1;

Now whenever a user class will access the data found in the custom property $self-{myProperties}> it will be automatically checked against.

In case it wasn't clear from the above example properties are handled/passed just as in traditional hash-based objects. This means that when the user class Foo is called it would be called just as it would be called traditionally (without the use of the OOP class), as such:

  use Foo;
  
  my $object = Foo->new({
                         one => {
                                 abye => 'Superman!'
                                },
                         two => 'foobar',
                         three => [1,2,3,4]
                        });
  
  $object->{one}->{goodbye} = 'Yes it is valid!';
  $object->{one}->{abye} = 'Sure we could overwrite an element!';
  $object->{one}->{maxLength} = 666;               # no access to definitions
  $object->{PROTOTYPE}->{one}->{maxLength} = 666;  # no access to definitions
  $object->{one}->{badbye} = 'This one would not be good as per prototype!';

Can you tell any difference? Of course not, because that is the intended effect. It should allow the developer of Foo to be able to distribute Foo, write documentation on what properties it takes, and have the peace of mind that the user using Foo will properly adhere to the intended usage.

So while the user cannot tell the difference in the usage of the Foo module, there is a great difference of what is happening behind the scenes. Unlike Foo without the OOP class, the OOP powered version gives peace of mind to both the user and developer of Foo by ensuring proper adherence to intended usage.

ACCESSORS

An important concept of Object Oriented Programming is the safe accessing of properties. In simple terms, rather than reading the data by accessing the property directly, in OOP one accesses the property by way of calling a method which in turn accesses the property. This is accomplished by way of "accessors".

The OOP class offers accessors that are quite generic in nature as to be most flexible. A list of the presently supported accessors are listed below:

getProperty

This is an extremely generic and simply accessor whose only task is to allow for a developer to access a property safely. This counteracts the readAccess prototype property when set to zero. In other words if the prototype says that readAccess is forbidden it merely forbids direct access. In such case one has to consciously access it via this accessor. It is merely a preventative measure to prevent accidental data overwrites, mixups, etc... by accessing the properties directly.

AUTHOR INFORMATION ^

Copyright 2007-Present, Milan Adamovsky. All rights reserved.

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

BUGS ^

Please report them to: milan@adamovsky.com.

SEE ALSO ^

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