The OOP in PHP

Matthew Turland

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I Co/Wrote These

http://phparch.com

http://sitepoint.com

Functions

Lots of Functions

Lots of Guards Too

Or logs full of this:

PHP Notice:  Undefined index: alpha
PHP Notice:  Undefined index: bravo
PHP Notice:  Undefined index: delta

Scope

"In computer programming, a scope is the context within a computer program in which an identifier is in effect, and can be resolved to an entity – when the entity is visible."

http://en.wikipedia.org/wiki/Scope_(computer_science)

See also: Variable Scope in the PHP manual

Debugging Globals is Hard

Conclusion: We need a level of scope beyond the global namespace and individual function scope.

A Better Way

Objects!

• Malleable containers for logic and data definitions
• Helpful for organizing code into semantically meaningful units
• Can limit when/how data can be stored and changed

Encapsulation

"Encapsulation is used to refer to one of two related but distinct notions, and sometimes to the combination thereof:

• A language mechanism for restricting access to some of the object's components.
• A language construct that facilitates the bundling of data with the methods (or other functions) operating on that data."

http://en.wikipedia.org/wiki/Encapsulation_(object-oriented_programming)

What's a Class?

• "Blueprint" for creating objects referred to as instances
• Collection of variable/property and function/method definitions
• Provides a level of scope shared across multiple functions

See also: The Basics in the PHP manual

Classes

Methods

Objects

Visibility

"Each person is three people in one: the person everyone sees, the person only close family and friends see, and the person only they see."

(Most likely paraphrased) Chinese proverb

See also: Visibility in the PHP manual

Public Access Modifier

Constants

See also: Constants in the PHP manual

Private Access Modifier

Be careful with these

Inheritance

"Inheritance is a way to establish is-a relationships between objects."

http://en.wikipedia.org/wiki/Inheritance_(object-oriented_programming)

Subclasses

parent::getTotal() calls this method defined in this class.

See also: Object Inheritance in the PHP manual

Protected Access Modifier

Polymorphism

"The primary usage of polymorphism... is the ability of objects belonging to different types to respond to method, field, or property calls of the same name, each one according to an appropriate type-specific behavior."

http://en.wikipedia.org/wiki/Polymorphism_in_object-oriented_programming

Class Typehints

See also: Type Hinting in the PHP manual

Abstraction

"Abstraction is the process by which data and programs are defined with a representation similar in form to its meaning (semantics), while hiding away the implementation details... a concept or idea not associated with any specific instance."

http://en.wikipedia.org/wiki/Abstraction_(computer_science)

Abstract Classes

See also: Class Abstraction in the PHP manual

Design by Contract

"Design by contract... is an approach for designing software. It prescribes that software designers should define formal, precise and verifiable interface specifications for software components... These specifications are referred to as 'contracts,' in accordance with a conceptual metaphor with the conditions and obligations of business contracts."

http://en.wikipedia.org/wiki/Design_by_contract

Interfaces

See also: Object Interfaces in the PHP manual

ArrayAccess Interface

See also: ArrayAccess in the PHP manual

Iterator Interface

See also: Iterator in the PHP manual

Don't Repeat Yourself

"Don't Repeat Yourself (DRY) is a principle of software development aimed at reducing repetition of information of all kinds... is stated as 'Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.'"

http://en.wikipedia.org/wiki/Don%27t_repeat_yourself

Horizontal Reuse

"Multiple inheritance is a feature... in which a class can inherit... features from more than one superclass. It is distinct from single inheritance, where a class may only inherit from one particular superclass."

http://en.wikipedia.org/wiki/Multiple_inheritance

"A mixin is a class which contains a combination of methods from other classes... not by inheritance... Mixins encourage code reuse and avoid well-known pathologies associated with multiple inheritance.

http://en.wikipedia.org/wiki/Mixin

"Traits are a mechanism for code reuse... by enabling a developer to reuse sets of methods freely in several independent classes living in different class hierarchies... and avoids the typical problems associated with multiple inheritance and mixins.

http://www.php.net/manual/en/language.oop5.traits.php

"Don't over-complicate this: traits are compiler-assisted copy-and-paste."

Rasmus Lerdorf, almost definitely paraphrased

Traits

See also: Traits in the PHP manual and the horizontal reuse RFC

Constructors and Destructors

Composition

"Object composition... is a way to combine simple objects or data types into more complex ones."

http://en.wikipedia.org/wiki/Object_composition

"Composition over inheritance... is a technique by which classes may achieve polymorphic behavior and code reuse by containing [instances of] other classes that implement the desired functionality instead of through inheritance.

http://en.wikipedia.org/wiki/Composition_over_inheritance

Dependency Injection

Dependency Injection Containers

More on this DIC implementation at pimple.sensiolabs.org

Autoloading

Example lifted from the PSR-0 standard

Check out this blog post on autoloading strategies

Classmaps

Use a script like this one to generate the classmap during your build process

Comparing Objects

See also: Comparing Objects

Cloning Objects

See also: Object Cloning and Objects and references in the PHP manual

Object Serialization

See also: Object Serialization in the PHP manual

Exceptions

See also: Exceptions

Beyond This Point

"Do not meddle in the affairs of dragons for you are crunchy and taste good with ketchup"

Final

Statics

Be careful with these

Magic Methods

"Magic" has the same connotation as "interesting" in the Chinese proverb.

Use these sparingly, intentionally, and with great hesitation.

See also: Magic Methods in the PHP manual

Property Magic Methods

Instance Magic Methods

Static Magic Methods

Serialization Magic Methods

String Magic Methods

Invocation Magic Methods

Resources

• PHP: Classes and Objects - Manual
• PHP Master: Write Cutting-Edge Code by Lorna Jane Mitchell, Davey Shafik, and Matthew Turland
• Designing Beautiful Software by Matthew Weier O'Phinney
• Your code sucks, let's fix it by Rafael Dohms
• Grumpy Programmer's Guide To Building Testable PHP Applications by Chris Hartjes
• Mastering Object Oriented PHP by Brandon Savage
• php|architect's Guide to PHP Design Patterns by Jason Sweat
• Patterns of Enterprise Application Architecture by Martin Fowler

SPL

• Elizabeth Smith's SPL in the Wild talk
• Elizabeth Smith's SPL to the Rescue slides
• My New SPL Features in PHP 5.3 slides

Where to Find Me

• matthewturland.com
• @elazar on Twitter
• elazar on GitHub
• Elazar on Freenode

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