Intermediate OOP in PHP

PHP World - November 13, 2014 David Stockton

@dstockto

What we’ll cover

Magic Methods

Polymorphism

Collections

Filtering Collections

SPL Iterator

What we’ll cover

SPL Count

SPL ArrayAccess

Listener Pattern

Loose Coupling

High Cohesion

Magic Methods

Methods all start with __

__construct & __destruct

__construct is called when you new up an object

Initialize object properties

Don’t do work!

__destruct is called when an object goes out of scope

Shut down connections, cleanup work

__call

__call($name, array $arguments)

Method called when method is called that is not in scope

Method doesn’t exist

Method is private / protected and called from outside object

__call

__callStatic

Just like __call but for static calls out of scope

Foo::createFromThing()

__get, __set, __isset, __unset

In many cases, if you need one, you need them all

Weird bugs if you don’t implement them all

__get

__get($name)

Called when reading an object property that’s not in scope

!

$value = $foo->madeUpValue;

__get

__set

__set($name, $value)

!

!

So, why do we need them all?

$foo->bar = ‘baz’;

$value = $foo->bar; // Get baz

if (isset($foo->bar)) { $value = $foo->bar; // Never get here if no __isset }

__isset

__isset($name)

isset($object->variable)

!

!

__unset

__unset($name)

unset($object->variable);

!

!

What you can do with them

Implement a class that doesn’t allow dynamic values

Implement a class that only allows values with certain naming conventions

Automatic calling of accessors (getters and setters)

The downsides

Harder to follow, no “ctrl-click” in IDEs

No auto-complete for __call or __callStatic methods in IDEs

Can use @method doc block to help

@method int add() add(numeric $a, numeric $b) Add numbers

@method docblock

__sleep & __wakeup

Called on serialize() and unserialize() calls

__sleep: Use to close connections, cleanup

__wakeup: Use to re-establish connections, setup

Why?

Some things in PHP are not serializable

__toString()

Retrieve string representation of a class

Must return a string

Cannot throw an exception

__toString

__toString

__clone

Create a new object based on an existing object

Called when clone is used:

$foo = clone $bar;

__clone

By default, clone is shallow

!

!

!

$foo = new Foo();

Foo$foo

Foo $bar$foo Bar

$foo2 = clone $foo;

Foo $bar$foo Bar

Foo $bar$bar

Now with __clone

$foo = new Foo();

Foo$foo

Foo $bar$foo Bar

$foo2 = clone $foo;

Foo $bar$foo Bar

Foo $bar$bar

__clone called on the clone

$foo2 = clone $foo;

Foo $bar$foo Bar

Foo $bar$bar Bar

__invoke

Allows an object to be used like a function or callable

Object can be built configured and then “executed”

__invoke

__invoke

__autoload

Don’t use __autoload, use spl_autoload_register

Called when a class, interface, or trait is used that hasn’t been loaded

Allows just in time loading of classes, no more requires and includes at the top of files

__set_state

Used with var_export

Allows setting of object variables from an array of input

__debugInfo

New in PHP 5.6

Controls output of var_dump

__debugInfo

var_dump

Add __debugInfo

var_dump again

PolymorphismAllow code to use different objects in the same

way

Speakableinterface

Polymorphism

Polymorphism

Collections and Polymorphism

Silverware Drawer

SilverwareContainerinterface

Silverwareinterface

Abstract Utensil Class

A Forking Example

Silver Spoons

Knife

Put silverware away

How many utensils?

Add method getNumberOfItems

!

!

Implement SPL Countable

- OR -

SPL Countable

How to use?

Retrieve Specific Utensils

SPL to the Rescue

Implement SPL ArrayAccess

Make our object work like an array

SPL ArrayAccess

SPL ArrayAccess

What does that allow?

Use an iterator: !

• Implement iterator • Extend one of these: • AppendIterator • ArrayIterator • CachingIterator • CallbackFilterIterator • InfiniteIterator • …etc.

Loop Over Utensils in Drawer

Easy wayExtend ArrayIterator

Add some silverware

Now what? Iterate it!

A new iterator

Only get clean utensils

SPLSubject / SPLObserverMoving right along

Implement SplSubject

Email class continued

Validate uses our observers

Build some observersInvalid Emails don’t send

Limit Sends by domains?

Put it all together

Loose Coupling

Loose Coupling

Minimize number of hard-coded dependencies

Type hint interfaces, not classes

Dependency Injection / Inversion of Control

Dependency Injection Simply

High CohesionDo one thing well

High Cohesion

Do one thing well

Methods

Classes

Packages / Namespaces

Everything the class does is related to the goal

–David Stockton

“If you have to use ‘and’ to describe what your method or class does,

it’s probably doing too much.”

Prefer Composition over Inheritance

Prefer Composition over Inheritance

Inheritance is not the only way to expand functionality of a class

Often it’s not even the best way

Photo Credits

• Lego Magician - https://www.flickr.com/photos/evaysucamara/5438832695 • Silverware - https://www.flickr.com/photos/jenny-pics/4128947072 • Fork - https://www.flickr.com/photos/naturesdawn/2507321223 • Trailer hitch - https://www.flickr.com/photos/jeremybrooks/2476396242 • The Glue Side of the Force - https://www.flickr.com/photos/st3f4n/4085958000 • Last Will and Testament - https://www.flickr.com/photos/ken_mayer/5599532152 • Guest Composer - https://www.flickr.com/photos/tamuc/12843465194

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Questions?