decon.xml

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<sect1 xml:id="language.oop5.decon" xmlns="http://docbook.org/ns/docbook">
 <title>Constructores y destructores</title>

 <sect2 xml:id="language.oop5.decon.constructor">
  <title>Constructor</title>
   <methodsynopsis xml:id="object.construct">
    <type>void</type><methodname>__construct</methodname>
    <methodparam rep="repeat"><type>mixed</type><parameter>values</parameter><initializer>""</initializer></methodparam>
   </methodsynopsis>
   <para>
    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.
   </para>
   <note>
    <simpara>
     Los constructores padres no son llamados implícitamente si la clase hija define
     un constructor. Para ejecutar un constructor padre, se requiere invocar a
     <function>parent::__construct</function> 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).
    </simpara>
   </note>
   <example>
    <title>Utilización de nuevos constructores unificados</title>
   <programlisting role="php">
<![CDATA[
<?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();
?>
]]>
    </programlisting>
   </example>
   <para>
    A diferencia de otros métodos, <link linkend="object.construct">__construct()</link>
    is exempt from the usual
    <link linkend="language.oop.lsp">signature compatibility rules</link>
    when being extended.
   </para>
   <para>
    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.
   </para>
   <example>
    <title>Using constructor arguments</title>
    <programlisting role="php">
<![CDATA[
<?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);
?>
]]>
    </programlisting>
   </example>
   <para>
    If a class has no constructor, or the constructor has no required arguments, the parentheses
    may be omitted.
   </para>
   <sect3>
    <title>Old-style constructors</title>
    <para>
     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 <constant>E_DEPRECATED</constant> error but still call that function as a constructor.
     If both <link linkend="object.construct">__construct()</link> and a same-name method are
     defined, <link linkend="object.construct">__construct()</link> will be called.
    </para>
    <para>
     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.
    </para>
    <para>Always use <link linkend="object.construct">__construct()</link> in new code.
    </para>
   </sect3>
   <sect3 xml:id="language.oop5.decon.constructor.promotion">
    <title>Constructor Promotion</title>
    <para>
     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.
    </para>
    <example>
     <title>Using constructor property promotion</title>
     <programlisting role="php">
<![CDATA[
<?php
class Point {
    public function __construct(protected int $x, protected int $y = 0) {
    }
}
]]>
     </programlisting>
    </example>
    <para>
     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.
    </para>
    <para>
     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.
    </para>
    <note>
     <para>
      Object properties may not be typed <type>callable</type> due to engine ambiguity that would
      introduce. Promoted arguments, therefore, may not be typed <type>callable</type> either. Any
      other <link linkend="language.types.declarations">type declaration</link> is permitted, however.
     </para>
    </note>
    <note>
     <para>
      <!-- This should be linked once attributes are documented. -->
      Attributes placed on a promoted constructor argument will be replicated to both the property
      and argument.
     </para>
    </note>
   </sect3>
   <sect3 xml:id="language.oop5.decon.constructor.static">
    <title>Static creation methods</title>
    <para>
     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.
    </para>
    <example>
     <title>Using static creation methods</title>
     <programlisting role="php">
<![CDATA[
<?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);
]]>
     </programlisting>
    </example>
    <para>
     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.
    </para>
    <para>
     The three public static methods then demonstrate different ways of instantiating the object.
    </para>
    <simplelist>
     <member><code>fromBasicData()</code> takes the exact parameters that are needed, then creates the
      object by calling the constructor and returning the result.</member>
     <member><code>fromJson()</code> 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.</member>
     <member><code>fromXml()</code> 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.</member>
    </simplelist>
    <para>
     In all three cases, the <code>static</code> keyword is translated into the name of the class the code is in.
     In this case, <code>Product</code>.
    </para>
   </sect3>
  </sect2>
 <sect2 xml:id="language.oop5.decon.destructor">
  <title>Destructor</title>
  <methodsynopsis xml:id="object.destruct">
   <type>void</type><methodname>__destruct</methodname>
   <void />
  </methodsynopsis>
  <para>
   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.
  </para>
  <example>
   <title>Ejemplo de Destructor</title>
   <programlisting role="php">
<![CDATA[
<?php

class MyDestructableClass
{
    function __construct() {
        print "En el constructor\n";
    }

    function __destruct() {
        print "Destruyendo " . __CLASS__ . "\n";
    }
}

$obj = new MyDestructableClass();

]]>
   </programlisting>
  </example>
  <para>
   Como los constructores, los destructores padre no serán llamados
   implícitamente por el motor. Para ejecutar un destructor padre, se
   deberá llamar explícitamente a <function>parent::__destruct</function>
   en el interior del destructor. También como los constructores, una clase child
   puede heredar el destructor de los padres si no implementa uno propio.
  </para>
  <para>
   El destructor será invocado aún si la ejecución del script es detenida
   usando <function>exit</function>. Llamar a <function>exit</function> en un
   destructor evitará que se ejecuten las rutinas restantes de finalización.
  </para>
  <note>
   <para>
    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).
   </para>
  </note>
  <note>
   <para>
    Intentar lanzar una excepción desde un destructor (invocado en la finalización
    del script) causa un error fatal.
   </para>
  </note>
 </sect2>

</sect1>

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