Post date: Jun 24, 2011 11:56:54 AM
Object interfaces allow you to create code which specifies which methods a class must implement, without having to define how these methods are handled.
Interfaces are defined using the interface keyword, in the same way as a standard class, but without any of the methods having their contents defined.
All methods declared in an interface must be public, this is the nature of an interface.
To implement an interface, the implements operator is used. All methods in the interface must be implemented within a class; failure to do so will result in a fatal error. Classes may implement more than one interface if desired by separating each interface with a comma.
Note:
A class cannot implement two interfaces that share function names, since it would cause ambiguity.
Note:
Interfaces can be extended like classes using the extends operator.
Note:
The class implementing the interface must use the exact same method signatures as are defined in the interface. Not doing so will result in a fatal error.
Its possible for interfaces to have constants. Interface constants works exactly like class constants except they cannot be overridden by a class/interface that inherits it.
Example #1 Interface example
<?php
// Declare the interface 'iTemplate'
interface iTemplate
{
public function setVariable($name, $var);
public function getHtml($template);
}
// Implement the interface
// This will work
class Template implements iTemplate
{
private $vars = array();
public function setVariable($name, $var)
{
$this->vars[$name] = $var;
}
public function getHtml($template)
{
foreach($this->vars as $name => $value) {
$template = str_replace('{' . $name . '}', $value, $template);
}
return $template;
}
}
// This will not work
// Fatal error: Class BadTemplate contains 1 abstract methods
// and must therefore be declared abstract (iTemplate::getHtml)
class BadTemplate implements iTemplate
{
private $vars = array();
public function setVariable($name, $var)
{
$this->vars[$name] = $var;
}
}
?>
Example #2 Extendable Interfaces
<?php
interface a
{
public function foo();
}
interface b extends a
{
public function baz(Baz $baz);
}
// This will work
class c implements b
{
public function foo()
{
}
public function baz(Baz $baz)
{
}
}
// This will not work and result in a fatal error
class d implements b
{
public function foo()
{
}
public function baz(Foo $foo)
{
}
}
?>
Example #3 Multiple interface inheritance
<?php
interface a
{
public function foo();
}
interface b
{
public function bar();
}
interface c extends a, b
{
public function baz();
}
class d implements c
{
public function foo()
{
}
public function bar()
{
}
public function baz()
{
}
}
?>
Example #4 Interfaces with constants
<?php
interface a
{
const b = 'Interface constant';
}
// Prints: Interface constant
echo a::b;
// This will however not work because its not allowed to
// override constants.
class b implements a
{
const b = 'Class constant';
}
?>
An interface, together with type-hinting, provides a good way to make sure that a particular object contains particular methods. See instanceof operator and type hinting.
Overloading in PHP provides means to dynamically "create" properties and methods. These dynamic entities are processed via magic methods one can establish in a class for various action types.
The overloading methods are invoked when interacting with properties or methods that have not been declared or are not visible in the current scope. The rest of this section will use the terms "inaccessible properties" and "inaccessible methods" to refer to this combination of declaration and visibility.
All overloading methods must be defined as public.
Note:
None of the arguments of these magic methods can be passed by reference.
Note:
PHP's interpretation of "overloading" is different than most object oriented languages. Overloading traditionally provides the ability to have multiple methods with the same name but different quantities and types of arguments.
Version
5.3.0
5.1.0
Description
Added __callStatic(). Added warning to enforce public visibility and non-static declaration.
Added __isset() and __unset().
void __set ( string $name , mixed $value )
mixed __get ( string $name )
bool __isset ( string $name )
void __unset ( string $name )
__set() is run when writing data to inaccessible properties.
__get() is utilized for reading data from inaccessible properties.
__isset() is triggered by calling isset() or empty() on inaccessible properties.
__unset() is invoked when unset() is used on inaccessible properties.
The $name argument is the name of the property being interacted with. The __set() method's $value argument specifies the value the $name'ed property should be set to.
Property overloading only works in object context. These magic methods will not be triggered in static context. Therefore these methods should not be declared static. As of PHP 5.3.0, a warning is issued if one of the magic overloading methods is declared static.
Note:
The return value of __set() is ignored because of the way PHP processes the assignment operator. Similarly, __get() is never called when chaining assignments together like this:
$a = $obj->b = 8;
Note:
It is not possible to use overloaded properties in other language constructs than isset(). This means if empty() is called on an overloaded property, the overloaded method is not called.
To workaround that limitation, the overloaded property must be copied into a local variable in the scope and then be handed to empty().
Example #1 Overloading properties via the __get(), __set(), __isset() and __unset() methods
<?php
class PropertyTest {
/** Location for overloaded data. */
private $data = array();
/** Overloading not used on declared properties. */
public $declared = 1;
/** Overloading only used on this when accessed outside the class. */
private $hidden = 2;
public function __set($name, $value) {
echo "Setting '$name' to '$value'\n";
$this->data[$name] = $value;
}
public function __get($name) {
echo "Getting '$name'\n";
if (array_key_exists($name, $this->data)) {
return $this->data[$name];
}
$trace = debug_backtrace();
trigger_error(
'Undefined property via __get(): ' . $name .
' in ' . $trace[0]['file'] .
' on line ' . $trace[0]['line'],
E_USER_NOTICE);
return null;
}
/** As of PHP 5.1.0 */
public function __isset($name) {
echo "Is '$name' set?\n";
return isset($this->data[$name]);
}
/** As of PHP 5.1.0 */
public function __unset($name) {
echo "Unsetting '$name'\n";
unset($this->data[$name]);
}
/** Not a magic method, just here for example. */
public function getHidden() {
return $this->hidden;
}
}
echo "<pre>\n";
$obj = new PropertyTest;
$obj->a = 1;
echo $obj->a . "\n\n";
var_dump(isset($obj->a));
unset($obj->a);
var_dump(isset($obj->a));
echo "\n";
echo $obj->declared . "\n\n";
echo "Let's experiment with the private property named 'hidden':\n";
echo "Privates are visible inside the class, so __get() not used...\n";
echo $obj->getHidden() . "\n";
echo "Privates not visible outside of class, so __get() is used...\n";
echo $obj->hidden . "\n";
?>
The above example will output:
Setting 'a' to '1' Getting 'a' 1 Is 'a' set? bool(true) Unsetting 'a' Is 'a' set? bool(false) 1 Let's experiment with the private property named 'hidden': Privates are visible inside the class, so __get() not used... 2 Privates not visible outside of class, so __get() is used... Getting 'hidden' Notice: Undefined property via __get(): hidden in <file> on line 70 in <file> on line 29
mixed __call ( string $name , array $arguments )
mixed __callStatic ( string $name , array $arguments )
__call() is triggered when invoking inaccessible methods in an object context.
__callStatic() is triggered when invoking inaccessible methods in a static context.
The $name argument is the name of the method being called. The $arguments argument is an enumerated array containing the parameters passed to the $name'ed method.
Example #2 Overloading methods via the __call() and __callStatic() methods
<?php
class MethodTest {
public function __call($name, $arguments) {
// Note: value of $name is case sensitive.
echo "Calling object method '$name' "
. implode(', ', $arguments). "\n";
}
/** As of PHP 5.3.0 */
public static function __callStatic($name, $arguments) {
// Note: value of $name is case sensitive.
echo "Calling static method '$name' "
. implode(', ', $arguments). "\n";
}
}
$obj = new MethodTest;
$obj->runTest('in object context');
MethodTest::runTest('in static context'); // As of PHP 5.3.0
?>
The above example will output:
Calling object method 'runTest' in object context Calling static method 'runTest' in static context