DevTut

# Magic Methods

# __call() and __callStatic()

__call() and __callStatic() are called when somebody is calling nonexistent object method in object or static context.

class Foo
{
    /**
     * This method will be called when somebody will try to invoke a method in object
     * context, which does not exist, like:
     *
     * $foo->method($arg, $arg1);
     *
     * First argument will contain the method name(in example above it will be "method"),
     * and the second will contain the values of $arg and $arg1 as an array.
     */
    public function __call($method, $arguments)
    {
        // do something with that information here, like overloading
        // or something generic.
        // For sake of example let's say we're making a generic class,
        // that holds some data and allows user to get/set/has via
        // getter/setter methods. Also let's assume that there is some
        // CaseHelper which helps to convert camelCase into snake_case.
        // Also this method is simplified, so it does not check if there
        // is a valid name or
        $snakeName = CaseHelper::camelToSnake($method);
        // Get get/set/has prefix
        $subMethod = substr($snakeName, 0, 3);

        // Drop method name.
        $propertyName = substr($snakeName, 4);

        switch ($subMethod) {
            case "get":
                return $this->data[$propertyName];
            case "set":
                $this->data[$propertyName] = $arguments[0];
                break;
            case "has":
                return isset($this->data[$propertyName]);
            default:
                throw new BadMethodCallException("Undefined method $method");
        }
    }

    /**
     * __callStatic will be called from static content, that is, when calling a nonexistent
     * static method:
     *
     * Foo::buildSomethingCool($arg);
     *
     * First argument will contain the method name(in example above it will be "buildSomethingCool"),
     * and the second will contain the value $arg in an array.
     *
     * Note that signature of this method is different(requires static keyword). This method was not
     * available prior PHP 5.3
     */
    public static function __callStatic($method, $arguments)
    {
        // This method can be used when you need something like generic factory
        // or something else(to be honest use case for this is not so clear to me).
        print_r(func_get_args());
    }
}

# Example:

$instance = new Foo();

$instance->setSomeState("foo");
var_dump($instance->hasSomeState());      // bool(true)
var_dump($instance->getSomeState());      // string "foo"

Foo::exampleStaticCall("test");
// outputs:
Array
(
    [0] => exampleCallStatic
    [1] => test
)

# __get(), __set(), __isset() and __unset()

Whenever you attempt to retrieve a certain field from a class like so:

$animal = new Animal();
$height = $animal->height;

PHP invokes the magic method __get($name), with $name equal to "height" in this case. Writing to a class field like so:

$animal->height = 10;

Will invoke the magic method __set($name, $value), with $name equal to "height" and $value equal to 10.

PHP also has two built-in functions isset(), which check if a variable exists, and unset(), which destroys a variable. Checking whether a objects field is set like so:

isset($animal->height);

Will invoke the __isset($name) function on that object. Destroying a variable like so:

unset($animal->height);

Will invoke the __unset($name) function on that object.

Normally, when you don't define these methods on your class, PHP just retrieves the field as it is stored in your class. However, you can override these methods to create classes that can hold data like an array, but are usable like an object:

class Example {
    private $data = [];

    public function __set($name, $value) {
        $this->data[$name] = $value;
    }

    public function __get($name) {
        if (!array_key_exists($name, $this->data)) {
            return null;
        }

        return $this->data[$name];
    }

    public function __isset($name) {
        return isset($this->data[$name]);
    }

    public function __unset($name) {
        unset($this->data[$name]);
    }
}

$example = new Example();

// Stores 'a' in the $data array with value 15
$example->a = 15;

// Retrieves array key 'a' from the $data array
echo $example->a; // prints 15

// Attempt to retrieve non-existent key from the array returns null
echo $example->b; // prints nothing

// If __isset('a') returns true, then call __unset('a')
if (isset($example->a)) {
    unset($example->a));
}

# empty() function and magic methods

Note that calling empty() (opens new window) on a class attribute will invoke __isset() because as the PHP manual states:

empty() is essentially the concise equivalent to !isset($var) || $var == false

# __construct() and __destruct()

__construct() is the most common magic method in PHP, because it is used to set up a class when it is initialized. The opposite of the __construct() method is the __destruct() method. This method is called when there are no more references to an object that you created or when you force its deletion. PHP's garbage collection will clean up the object by first calling its destructor and then removing it from memory.

class Shape {
    public function __construct() {
        echo "Shape created!\n";
    }
}

class Rectangle extends Shape {
    public $width;
    public $height;

    public function __construct($width, $height) {
        parent::__construct();

        $this->width = $width;
        $this->height = $height;
        echo "Created {$this->width}x{$this->height} Rectangle\n"; 
    }

    public function __destruct() {
        echo "Destroying {$this->width}x{$this->height} Rectangle\n";
    }
}

function createRectangle() {
    // Instantiating an object will call the constructor with the specified arguments
    $rectangle = new Rectangle(20, 50);

    // 'Shape Created' will be printed
    // 'Created 20x50 Rectangle' will be printed
}

createRectangle();
// 'Destroying 20x50 Rectangle' will be printed, because
// the `$rectangle` object was local to the createRectangle function, so
// When the function scope is exited, the object is destroyed and its
// destructor is called.

// The destructor of an object is also called when unset is used:
unset(new Rectangle(20, 50));

# __toString()

Whenever an object is treated as a string, the __toString() method is called. This method should return a string representation of the class.

class User {
    public $first_name;
    public $last_name;
    public $age;

    public function __toString() {
        return "{$this->first_name} {$this->last_name} ($this->age)";
    }
}

$user = new User();
$user->first_name = "Chuck";
$user->last_name = "Norris";
$user->age = 76;

// Anytime the $user object is used in a string context, __toString() is called

echo $user; // prints 'Chuck Norris (76)'

// String value becomes: 'Selected user: Chuck Norris (76)'
$selected_user_string = sprintf("Selected user: %s", $user);

// Casting to string also calls __toString()
$user_as_string = (string) $user;

# __clone()

__clone is invoked by use of the clone keyword. It is used to manipulate object state upon cloning, after the object has been actually cloned.

class CloneableUser
{
    public $name;
    public $lastName;

    /**
     * This method will be invoked by a clone operator and will prepend "Copy " to the
     * name and lastName properties.
     */
    public function __clone()
    {
        $this->name = "Copy " . $this->name;
        $this->lastName = "Copy " . $this->lastName;
    }
}

Example:

$user1 = new CloneableUser();
$user1->name = "John";
$user1->lastName = "Doe";

$user2 = clone $user1; // triggers the __clone magic method

echo $user2->name;     // Copy John
echo $user2->lastName; // Copy Doe

# __invoke()

This magic method is called when user tries to invoke object as a function. Possible use cases may include some approaches like functional programming or some callbacks.

class Invokable
{
    /**
     * This method will be called if object will be executed like a function:
     *
     * $invokable();
     *
     * Args will be passed as in regular method call.
     */
    public function __invoke($arg, $arg, ...)
    {
        print_r(func_get_args());
    }
}

// Example:
$invokable = new Invokable();
$invokable([1, 2, 3]);

// optputs:
Array
(
    [0] => 1
    [1] => 2
    [2] => 3
)

# __sleep() and __wakeup()

__sleep and __wakeup are methods that are related to the serialization process. serialize function checks if a class has a __sleep method. If so, it will be executed before any serialization. __sleep is supposed to return an array of the names of all variables of an object that should be serialized.

__wakeup in turn will be executed by unserialize if it is present in class. It's intention is to re-establish resources and other things that are needed to be initialized upon unserialization.

class Sleepy {
    public $tableName;
    public $tableFields;
    public $dbConnection;

    /**
     * This magic method will be invoked by serialize function.
     * Note that $dbConnection is excluded.
     */
    public function __sleep()
    {
        // Only $this->tableName and $this->tableFields will be serialized.
        return ['tableName', 'tableFields'];
    }

    /**
     * This magic method will be called by unserialize function.
     *
     * For sake of example, lets assume that $this->c, which was not serialized,
     * is some kind of a database connection. So on wake up it will get reconnected.
     */
    public function __wakeup()
    {
        // Connect to some default database and store handler/wrapper returned into
        // $this->dbConnection
        $this->dbConnection = DB::connect();
    }
}

# __debugInfo()

This method is called by var_dump() when dumping an object to get the properties that should be shown. If the method isn't defined on an object, then all public, protected and private properties will be shown. — PHP Manual (opens new window)

class DeepThought {
    public function __debugInfo() {
        return [42];
    }
}


var_dump(new DeepThought());

The above example will output:

class DeepThought#1 (0) {
}


var_dump(new DeepThought());

The above example will output:

class DeepThought#1 (1) {
  public ${0} =>
  int(42)
}

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