PHP permite a los desarrolladores declarar métodos constructores para las clases. Aquellas que tengan un método constructor lo invocarán en cada nuevo objeto creado, lo que lo hace idóneo para cualquier inicialización que el objeto pueda necesitar antes de ser usado.
Nota: Los constructores padres no son llamados implícitamente si la clase hija define un constructor. Para ejecutar un constructor padre, se requiere invocar a parent::__construct() desde el constructor hijo. Si el hijo no define un constructor, entonces se puede heredar de la clase madre como un método de clase normal (si no fue declarada como privada).
Ejemplo #1 Utilización de nuevos constructores unificados
<?php
class BaseClass {
function __construct() {
print "En el constructor BaseClass\n";
}
}
class SubClass extends BaseClass {
function __construct() {
parent::__construct();
print "En el constructor SubClass\n";
}
}
class OtherSubClass extends BaseClass {
// heredando el constructor BaseClass
}
// En el constructor BaseClass
$obj = new BaseClass();
// En el constructor BaseClass
// En el constructor SubClass
$obj = new SubClass();
// En el constructor BaseClass
$obj = new OtherSubClass();
?>A diferencia de otros métodos, __construct() is exempt from the usual signature compatibility rules when being extended.
Constructors are ordinary methods which are called during the instantiation of their corresponding object. As such, they may define an arbitrary number of arguments, which may be required, may have a type, and may have a default value. Constructor arguments are called by placing the arguments in parentheses after the class name.
Ejemplo #2 Using constructor arguments
<?php
class Point {
protected int $x;
protected int $y;
public function __construct(int $x, int $y = 0) {
$this->x = $x;
$this->y = $y;
}
}
// Pass both parameters.
$p1 = new Point(4, 5);
// Pass only the required parameter. $y will take its default value of 0.
$p2 = new Point(4);
// With named parameters (as of PHP 8.0):
$p3 = new Point(y: 5, x: 4);
?>If a class has no constructor, or the constructor has no required arguments, the parentheses may be omitted.
Prior to PHP 8.0.0, classes in the global namespace will interpret a method named the same as the class as an old-style constructor. That syntax is deprecated, and will result in an E_DEPRECATED error but still call that function as a constructor. If both __construct() and a same-name method are defined, __construct() will be called.
In namespaced classes, or any class as of PHP 8.0.0, a method named the same as the class never has any special meaning.
Always use __construct() in new code.
As of PHP 8.0.0, constructor parameters may also be promoted to correspond to an object property. It is very common for constructor parameters to be assigned to a property in the constructor but otherwise not operated upon. Constructor promotion provides a short-hand for that use case. The example above could be rewritten as the following.
Ejemplo #3 Using constructor property promotion
<?php
class Point {
public function __construct(protected int $x, protected int $y = 0) {
}
}When a constructor argument includes a visibility modifier, PHP will interpret it as both an object property and a constructor argument, and assign the argument value to the property. The constructor body may then be empty or may contain other statements. Any additional statements will be executed after the argument values have been assigned to the corresponding properties.
Not all arguments need to be promoted. It is possible to mix and match promoted and not-promoted arguments, in any order. Promoted arguments have no impact on code calling the constructor.
Nota:
Object properties may not be typed callable due to engine ambiguity that would introduce. Promoted arguments, therefore, may not be typed callable either. Any other type declaration is permitted, however.
Nota:
Attributes placed on a promoted constructor argument will be replicated to both the property and argument.
PHP only supports a single constructor per class. In some cases, however, it may be desirable to allow an object to be constructed in different ways with different inputs. The recommended way to do so is by using static methods as constructor wrappers.
Ejemplo #4 Using static creation methods
<?php
class Product {
private ?int $id;
private ?string $name;
private function __construct(?int $id = null, ?string $name = null) {
$this->id = $id;
$this->name = $name;
}
public static function fromBasicData(int $id, string $name): static {
$new = new static($id, $name);
return $new;
}
public static function fromJson(string $json): static {
$data = json_decode($json);
return new static($data['id'], $data['name']);
}
public static function fromXml(string $xml): static {
// Put your own logic here.
$data = convert_xml_to_array($xml);
$new = new static();
$new->id = $data['id'];
$new->name = $data['name'];
return $new;
}
}
$p1 = Product::fromBasicData(5, 'Widget');
$p2 = Product::fromJson($some_json_string);
$p3 = Product::fromXml($some_xml_string);The constructor may be made private or protected to prevent it from being called externally. If so, only a static method will be able to instantiate the class. Because they are in the same class definition they have access to private methods, even if not of the same object instance. The private constructor is optional and may or may not make sense depending on the use case.
The three public static methods then demonstrate different ways of instantiating the object.
fromBasicData() takes the exact parameters that are needed, then creates the object by calling the constructor and returning the result.fromJson() accepts a JSON string and does some pre-processing on it itself to convert it into the format desired by the constructor. It then returns the new object.fromXml() accepts an XML string, preprocesses it, and then creates a bare object. The constructor is still called, but as all of the parameters are optional the method skips them. It then assigns values to the object properties directly before returning the result. In all three cases, the static keyword is translated into the name of the class the code is in. In this case, Product.
PHP posee un concepto de destructor similar al de otros lenguajes orientados a objetos, tal como C++. El método destructor será llamado tan pronto como no hayan otras referencias a un objeto determinado, o en cualquier otra circunstancia de finalización.
Ejemplo #5 Ejemplo de Destructor
<?php
class MyDestructableClass
{
function __construct() {
print "En el constructor\n";
}
function __destruct() {
print "Destruyendo " . __CLASS__ . "\n";
}
}
$obj = new MyDestructableClass();Como los constructores, los destructores padre no serán llamados implícitamente por el motor. Para ejecutar un destructor padre, se deberá llamar explícitamente a parent::__destruct() en el interior del destructor. También como los constructores, una clase child puede heredar el destructor de los padres si no implementa uno propio.
El destructor será invocado aún si la ejecución del script es detenida usando exit(). Llamar a exit() en un destructor evitará que se ejecuten las rutinas restantes de finalización.
Nota:
Los destructores invocados durante la finalización del script tienen los headers HTTP ya enviados. El directorio de trabajo en la fase de finalización del script puede ser diferente con algunos SAPIs (por ej., Apache).
Nota:
Intentar lanzar una excepción desde un destructor (invocado en la finalización del script) causa un error fatal.