PHP 5 Magic Methods

PHP 5 Magic Functions
Front Range PHP Users Group
http://frontrangephp.org/
February 10, 2010

PHP 5 Magic Functions
All functions start with __
PHP reserves all function names starting with __
Don’t define them unless you want the magic functionality

Magic Methods in this Presentation
__construct()
__destruct()
__toString()
__get()
__set()
__isset()
__unset()
__call()
__clone
__set_state()

Magic Methods briefly covered
__callStatic()
__sleep()
__wakeup()
__invoke()
__autoload()

New to PHP 5
Magic functions (in general) allow you to define class functionality without needing to duplicate code
I say in general since some of them don’t really seem to follow that definition and I didn’t find a definition that covers them all.

__construct()
If you’ve done any OOP in PHP5, you’ve probably run into this method.
Used to initialize an object.
Best practices say to make sure you don’t do work in the constructor.
Just assign values
… and remember Dependency Injection (coming up next)

__construct()
Constructor is setting values, but not doing work

__construct()
Doing work in constructors makes it harder to reuse the class.

__construct()
If you don’t provide a constructor method, and extend a class, the parent constructor will be called automatically.
If you do provide a constructor, and want the parent constructor called, you must called parent::__construct()

__construct()
By making the constructor inaccessible, you can prevent external instantiation.
For example, implementing the singleton pattern, we don’t want external instantiation since we cannot control how many objects are created.

__destruct()
__destruct() is called when
all references to an object are removed
object is explicitly destroyed
shutdown sequence is initiated

__destruct()
Parent destructors must be called explicitly if destructor is provided

__destruct()
You could use this method to ensure an object logs itself.

__destruct()
The destructor is called even if a script exits due to a call to exit()
However, if you call exit() in a destructor, the other destructors will be skipped.
Throwing an exception in the destructor is a fatal error.

__toString()
Called whenever you try to use an object in a string context

__toString()

__toString()
You can invoke via echo, print, *printf
Cast to string
$var = (string)$obj;

__toString()
__toString() cannot throw an exception – results in a fatal error
If you call functions or methods in your __toString() that can throw an exception, make sure you handle it within the __toString() method

__get()
Called when code tries to access non-accessible properties

__get()
Non-accessible can mean either the property is not defined or that it is not public
If it’s not defined, then __get() will be called from both inside and outside of the class context

__get()

__get()
Classes don’t even have to have properties

__get()
You could even use it to process values…

__set()
Called when code tries to set a property that is not accessible.
Not accessible can mean not defined or not public

__set()

__set()
If __set() is used to set a property that doesn’t exist, the new property will be public.
If it is used on a property that is not public, the accessibility will not change

__set()
Use it to validate values as they are passed in

__set()
If you want only the values you defined to be used in a class, set that behavior in __set().

__isset()
Called when isset() is called on an inaccessible property
If you’re using __set() and __get(), not defining __isset() can lead to some really weird errors.

__isset()

__isset()
How can this be?
You can retrieve the value, but it’s not set?
Must define
__isset()

__unset()
Called when code tries to unset a non-accessible value.
Without __unset()

__unset()
With __unset()

__call()
Called when a method is called that is not accessible.

__call()
Use it to extend a class and make everything public…

__call()
Yes, I didn’t extend anything in that example, but the principle is the same

__call()
Virtual Getters and Setters

__call()
All sorts of other uses for __call()

__clone()
Used if custom clone() behavior is needed
If clone() is called on an object that contains other objects, both the clone and the original contain the same objects.
Define __clone() to define what happens when an object is cloned

__clone()
Default Clone behavior
Using === to show they are the same

__clone()
Now with custom __clone()

__clone()
In the previous example we are comparing the objects
Even if the number value is the same, there are still two different objects

__set_state()
Used to set the state of an object when var_export code is used.

__set_state()
var_export() creates runnable PHP code.
So what happens when we run it?

__set_state()
So let’s define it

__set_state()
Why the differences?
stdClass doesn’t have a __set_state()
Since $val is protected, I need a setter.
Plus it shows how to deal with non-public stuff

Brief Look at other magic methods
You’ve already seen 48 slides, and chances are it’s getting close to an hour…
So here’s a quick overview of a few more of the magic methods

__callStatic()
New in PHP 5.3
Very similar to __call()
Intended for when a method is called in a static context (inaccessible method)
SomeClass::protectedStaticMethod();

__sleep()
Called when an object is serialized with PHP’s serialize.
Can be used to shutdown and remove resources (like database connections) which cannot be serialized

__wakeup()
Called when an object is unserialized.
Can be used to re-establish connections and re-initialize resources
ie, reconnect to the database

__invoke()
New in PHP 5.3
Allows you to treat an object like a function

__autoload()
Everyone using PHP 5 should be using this, or at least some form of autoloading.
Allows you to automatically load PHP files when they are needed.
No more need for require_once or include_once in your scripts

Q & A
Any questions?

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PHP 5 Magic Methods

by David Stockton

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PHP 5 Magic Methods Presentation Transcript