Getters and Setters

Intro

Abstraction and encapsulation are two sides of the same coin. Abstraction focuses on the outside fundamental characteristics which define and distinguish and object while encpasulation focuses on hiding the implementation of an Object's functionality; thereby freeing the Object's method's client or consumer of the need to understand the underlying complexity.

As far as a client is concerned an object is just a black box. It has methods which can retrieve and update state values but the internal implementation of all functionality should be completely hidden.

And this is the way we want it. Information hiding is one of the reasons that object oriented design scales to programming-in-the-colossal. It allows us to free our minds of so many lower levels of complexity and only focus on the highest levels of abstraction.

Thoughts on getters and setters

It's often said that in a properly encapsulated object no outside entity could directly access and/or change any of the object's instance variables.

Objective-C & Cocoa

In Objective-C and Cocoa for example when you are defining the class's interface you can have the compiler synthesize getter and setter methods like so

@interface Profile : NSObject
@property NSString *name;
- (id) initWithName:(NSString *) name;
@end

// Now imagine there is an implementation file for this interface with property
// and custom init method. Now to create a Profile object
Profile *myProfile = [[Profile alloc] initWithName:@"carlos cardona"];

That will handle creating two methods which allow me to access (get) and change (set) the value of name like so

NSLog(@"%@", [myProfile name]);
// logs "carlos cardona"
[myProfile setName:@"soljah cardona"];
// changes name from "carlos cardona" to "soljah cardona"

There are ways to be more restrictive and only synthesize a getter.

Ruby

Ruby is similar in the sense that you'll get an error if you try to get or set an instance variable without declaring a getter and/or setter.

class Profile
  def initialize(name)
    @name = name
  end
end

# now create a new Profile object
newProfile = Profile.new "carlos cardona"
# #<Profile:0x007ffc042fb040 @name="carlos cardona">

# now notice the fail if I try to get the value of name
newProfile.name
# NoMethodError: undefined method `name' for #<Profile:0x007ffc042fb040 @name="carlos cardona">

# the same thing if I try to set the value
newProfile.name = 'soljah cardona'
# NoMethodError: undefined method `name=' for #<Profile:0x007ffc042fb040 @name="carlos cardona">

You can manually create the getters and setters

class Profile
  def initialize(name)
    @name = name
  end
  def name
    @name
  end
  def name=(name)
    @name = name 
  end
end

This works but it's verbose. Ruby gives us a more pleasant way to do it.

class Profile
  attr_reader :name
  attr_writer :name
  def initialize(name)
    @name = name
  end
end

But of course Ruby takes it one step further

class Profile
  attr_accessor:name
  def initialize(name)
    @name = name
  end
end

The attr_reader, attr_writer, and attr_accessor methods leverage Ruby's terse yet expressive syntax to get more done with less code.

Intermission #1

So far Objective-C and Ruby have shown good language enforced abstraction and encapsulation. By design a property cannot be directly accessed and manipulated. Only through getter and setter methods explicitly provided by a Class's designer can a client of the object get access to state values.

It's worth a quick note on a couple specifics for later reference. In Objective-C and Cocoa when you have the compiler synthesize accessor methods for a property foo it will automatically give the getter and setter names foo and setFoo respectively.

In Ruby both the getter and the setter share the name of the property foo. Ex: Profile.foo

Now let's look at how PHP and Javascript do it.

PHP

PHP has poor language enforcement with regards to abstraction and encapsulation in this context.

A PHP Object's instance variables (when the visibility is public) are avaliable via the property name similar to Ruby.

What is not similar to Ruby is that this behavior is on by default as opposed to being turned on by the attr_accessor method.

<?php
class Profile{
  public $name = 'carlos cardona';
}

// Create a Profile Object
$profile = new Profile();

// getter
var_dump($profile->name);
// string(14) "carlos cardona"  

// setter
$profile->name = 'soljah cardona';
var_dump($profile->name);
// string(14) "soljah cardona"
?>

Javascript acts the same way.

Javascript

Javascript exhibits the same behavior as PHP in this context. It allows an object's properties to be accessed and updated via the property name out of the box.

<script>
function Profile(){
  this.name = 'carlos cardona';
}

// create a Profile Object.
var profile = new Profile();

// getter
console.log(profile.name);
// carlos cardona

//setter
profile.name = 'soljah cardona';
console.log(profile.name);
// soljah cardona
<script>

Final Thoughts

There are really two ways to consider this.

Side One

First is to say with regards to Abstraction and Encapsulation in the context of an Object's publicly visible properties via accessor methods Objective-C and Ruby exhibit better default behavior compared to PHP and Javascript.

This argument would be based on the fact that both Objective-C and Ruby require the developer to explicitly allow the client of the Object to have access to it's properties. Even then that access is only available via a method and never directly as seen in Objective C's setPropertyName method.

PHP and Javascript on the other hand allow direct access and manipulation of an Objects public properties by default thus they exhibit inferior behavior.

Side Two

The other way to consider this is that the true expressive power of javascript comes from it's dynamic nature. The ceremony that comes with allowing someone to access a property is just baggage.

After all doesn't Ruby just generate getter and setter methods which are the name of the property? That's what both javascript and PHP do out of the box!

More info

• What is attr_accessor in Ruby?

Published

Tags

• code 21
• php 3
• ruby 7
• javascript 12
• objectivec 2
• cocoa 1