PHP: Clases anónimas

Clases anónimas

En PHP 7 se ha añadido soporte para clases anónimas. Las clases anónimas son útiles cuando es necesario crear objetos sencillos y únicos.

<?php

// Código anterior a PHP 7
class Logger
{
    public function log($msg)
    {
        echo $msg;
    }
}

$util->setLogger(new Logger());

// Código de PHP 7+
$util->setLogger(new class {
    public function log($msg)
    {
        echo $msg;
    }
});

Pueden pasar argumentos a través de sus constructores, extender otras clases, implementar interfaces, y utilizar rasgos al igual que una clase normal:

<?php

class SomeClass {}
interface SomeInterface {}
trait SomeTrait {}

var_dump(new class(10) extends SomeClass implements SomeInterface {
    private $num;

    public function __construct($num)
    {
        $this->num = $num;
    }

    use SomeTrait;
});

El resultado del ejemplo sería:

object(class@anonymous)#1 (1) {
  ["Command line code0x104c5b612":"class@anonymous":private]=>
  int(10)
}

El anidamiento de una clase anónima dentro de otra clase no le proporciona acceso a ningún método o propiedad privados o protegidos de la clase externa. Para utilizar las propiedades o métodos protegidos de la clase externa, la clase anónima puede extender la clase externa. Para utilizar las propiedades privadas de la clase externa en la clase anónima, estos deben pasarse a su constructor:

<?php

class Externa
{
    private $prop = 1;
    protected $prop2 = 2;

    protected function func1()
    {
        return 3;
    }

    public function func2()
    {
        return new class($this->prop) extends Externa {
            private $prop3;

            public function __construct($prop)
            {
                $this->prop3 = $prop;
            }

            public function func3()
            {
                return $this->prop2 + $this->prop3 + $this->func1();
            }
        };
    }
}

echo (new Externa)->func2()->func3();

El resultado del ejemplo sería:

Todos los objetos creados por la misma declaración de clase anónima son instancias de esa misma clase.

<?php
function clase_anónima()
{
    return new class {};
}

if (get_class(clase_anónima()) === get_class(clase_anónima())) {
    echo 'misma clase';
} else {
    echo 'clase diferente';
}

El resultado del ejemplo sería:

misma clase

Nota:
Observe que el motor le asigna un nombre a las clases anónimas, como se demuestra en el siguiente ejemplo. Este nombre name ha de considerarse un detalle de implementación del cual no se debería depender.
<?php echo get_class(new class {});

El resultado del ejemplo sería algo similar a:
class@anonymous/in/oNi1A0x7f8636ad2021

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User Contributed Notes 8 notes

down

Anonymous ¶

8 years ago

Below three examples describe anonymous class with very simple and basic but quite understandable example

<?php
// First way - anonymous class assigned directly to variable
$ano_class_obj = new class{
    public $prop1 = 'hello';
    public $prop2 = 754;
    const SETT = 'some config';

    public function getValue()
    {
        // do some operation
        return 'some returned value';
    }

    public function getValueWithArgu($str)
    {
        // do some operation
        return 'returned value is '.$str;
    }
};

echo "\n";

var_dump($ano_class_obj);
echo "\n";

echo $ano_class_obj->prop1;
echo "\n";

echo $ano_class_obj->prop2;
echo "\n";

echo $ano_class_obj::SETT;
echo "\n";

echo $ano_class_obj->getValue();
echo "\n";

echo $ano_class_obj->getValueWithArgu('OOP');
echo "\n";

echo "\n";

// Second way - anonymous class assigned to variable via defined function
$ano_class_obj_with_func = ano_func();

function ano_func()
{
    return new class {
        public $prop1 = 'hello';
        public $prop2 = 754;
        const SETT = 'some config';

        public function getValue()
        {
            // do some operation
            return 'some returned value';
        }

        public function getValueWithArgu($str)
        {
            // do some operation
            return 'returned value is '.$str;
        }
    };
}

echo "\n";

var_dump($ano_class_obj_with_func);
echo "\n";

echo $ano_class_obj_with_func->prop1;
echo "\n";

echo $ano_class_obj_with_func->prop2;
echo "\n";

echo $ano_class_obj_with_func::SETT;
echo "\n";

echo $ano_class_obj_with_func->getValue();
echo "\n";

echo $ano_class_obj_with_func->getValueWithArgu('OOP');
echo "\n";

echo "\n";

// Third way - passing argument to anonymous class via constructors
$arg = 1; // we got it by some operation
$config = [2, false]; // we got it by some operation
$ano_class_obj_with_arg = ano_func_with_arg($arg, $config);

function ano_func_with_arg($arg, $config)
{
    return new class($arg, $config) {
        public $prop1 = 'hello';
        public $prop2 = 754;
        public $prop3, $config;
        const SETT = 'some config';

        public function __construct($arg, $config)
        {
            $this->prop3 = $arg;
            $this->config =$config;
        }

        public function getValue()
        {
            // do some operation
            return 'some returned value';
        }

        public function getValueWithArgu($str)
        {
            // do some operation
            return 'returned value is '.$str;
        }
    };
}

echo "\n";

var_dump($ano_class_obj_with_arg);
echo "\n";

echo $ano_class_obj_with_arg->prop1;
echo "\n";

echo $ano_class_obj_with_arg->prop2;
echo "\n";

echo $ano_class_obj_with_arg::SETT;
echo "\n";

echo $ano_class_obj_with_arg->getValue();
echo "\n";

echo $ano_class_obj_with_arg->getValueWithArgu('OOP');
echo "\n";

echo "\n";

down

ytubeshareit at gmail dot com ¶

7 years ago

Anonymous classes are syntax sugar that may appear deceiving to some.
The 'anonymous' class is still parsed into the global scope, where it is auto assigned a name, and every time the class is needed, that global class definition is used.  Example to illustrate....

The anonymous class version...
<?php

function return_anon(){
    return new class{
         public static $str="foo";  
    };
}
$test=return_anon();
echo $test::$str; //ouputs foo

//we can still access the 'anon' class directly in the global scope! 
$another=get_class($test); //get the auto assigned name
echo $another::$str;    //outputs foo
?>

The above is functionally the same as doing this....
<?php
class I_named_this_one{
    public static $str="foo";
}
function return_not_anon(){
    return 'I_named_this_one';
}
$clzz=return_not_anon();//get class name
echo $clzz::$str;
?>

down

sebastian.wasser at gmail ¶

5 years ago

I wanted to share my findings on static properties of anonymous classes.

So, given an anonymous class' object generating function like this:

<?php
function nc () {
    return new class {
        public static $prop = [];
    };
}
?>

Getting a new object and changing the static property:

<?php
$a = nc();
$a::$prop[] = 'a';

var_dump($a::$prop);
// array(1) {
//   [0] =>
//   string(1) "a"
// }
?>

Now getting another object and changing the static property will change the original one, meaning that the static property is truly static:

<?php
$b = nc();
$b::$prop[] = 'b';

var_dump($b::$prop); // Same as var_dump($a::$prop);
// array(2) {
//   [0] =>
//   string(1) "a"
//   [1] =>
//   string(1) "b"
// }

assert($a::$prop === $b::$prop); // true
?>

down

joey ¶

5 years ago

The only way to type hint this would appear to be as object.

If you need multiple instances of an anonymous class in a function you can use:

$class = function(string $arg):object {
    return new class($arg) {
        public function __construct(string $arg) {
            $this->ow = $arg;
        }
    };
};

Though for the sake of structure it's ill advised to do something like this outside of a single scope or that's used across multiple files. If you class is only used in one scope however then it's probably not a code mess problem.

down

j.m \ jamesweb \ ca ¶

7 years ago

/* I like the idea of OneShot classes.
Thanks to that Anonymous bro\sist for precising   
new class( $a, $b )
¯¯¯¯¯¯¯¯¯

If you are looking for "Delayed OneShot Anonymous Classes" for any reason (like the reason: loading files in a readable manner while not using autoload), it would probably look something like this; */

$u = function()use(&$u){
    $u = new class{private $name = 'Utils';};
};

$w = function(&$rewrite)use(&$w){
    $w = null;
    $rewrite = new class{private $name = 'DataUtils';};
};

// Usage;
var_dump(
    array(
        'Delayed',
        '( Self Destructive )',
        'Anonymous Class Creation',
        array(
            'Before ( $u )' => $u,
            'Running ( $u() )' => $u(),
            'After ( $u )' => $u,
        ),
        0,0,
        0,0,
        0,0,
        'Delayed',
        '( Overwriting && Self Destructive )',
        'Anonymous Class Creation',
        array(
            'Before ( $w )' => $w,
            'Running ( $w($u) )' => $w($u),
            'After ( $w )' => $w,
            'After ( $u )' => $u
        )
    )
);

// btw : oh shoot I failed a spam challenge

down

razvan_bc at yahoo dot com ¶

4 years ago

you can try these

<?php 

$oracle=&$_['nice_php'];
$_['nice_php']=(function(){
    return new class{
        public static function say($msg){
            echo $msg;
        }

        public static function sp(){
            echo self::say(' ');
        }

    };
});

/*
$_['nice_php']()::say('Hello');
$_['nice_php']()::sp();
$_['nice_php']()::say('World');
$_['nice_php']()::sp();
$_['nice_php']()::say('!');
//almost the same code bottom
*/

$oracle()::say('Hello');
$oracle()::sp();
$oracle()::say('World');
$oracle()::sp();
$oracle()::say('!');
?>

down

piotr at maslosoft dot com ¶

7 years ago

Please note that class name returned by `get_class` might contain null bytes, as is the case in my version of PHP (7.1.4). 

Name will change when class starting line or it's body is changed.

Yes, name is implementation detail that should not be relied upon, but in some rare use cases it is required (annotating anonymous class).

down

ismaelj+php at hotmail dot com ¶

2 months ago

Thanks to the new property hooks in PHP 8.4 (https://wiki.php.net/rfc/property-hooks) and anonymous functions, now we can create an inner class instantiated only on use:

<?php
class BaseClass {
  public function __construct() { echo "base class\n"; }

  public $childClass  { set {}  get {
    if ($this->childClass === null ) {
      $this->childClass = new class {
        public function __construct() { echo "  child class\n"; }
        public function say(string $s) : void { echo "     $s\n"; }
      };
    }

    return $this->childClass;
    }
  }
}

$base = new BaseClass();

$base->childClass->say('Hello');
$base->childClass->say('World');

/*
Output:

base class
  child class
     Hello
     World
*/
?>

The obvious downside is that you can't set a type to the child class, unless  you define an interface and the child class implements it or if the child class extends an existing class:

<?php
class ParentClass {
  public function say(string $s) : void { echo "     $s\n"; }
}

class BaseClass {
  public function __construct() { echo "base class\n"; }

  public ParentClass $childClass { set {}  get {
    if (!isset($this->childClass)) {
      $this->childClass = new class extends ParentClass {
        public function __construct() { echo "  child class\n"; }
      };
    }

    return $this->childClass;
    }
  }
}

$base = new BaseClass();

$base->childClass->say('Hello');
$base->childClass->say('World');

/*
Output:

base class
  child class
     Hello
     World
*/
?>
?>

This can be also done with functions, but  with hooks to me looks more like in other languages that have this functionality natively.

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