PHP_EXTENSION_METHODS

Copyright (c) 2016 Antonio Walter (antoniowcr@gmail.com)

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<?php

namespace Pattern\Extension;

/**
 * API for extension methods in PHP (like C#).
 */
class Extension
{
    /**
     * Apply extension to an instance.
     *
     * @param object $instance
     * @return \Pattern\Extension\ExtensionWrapper
     */
    public function __invoke($instance)
    {
        return Extension::apply($instance);
    }

    /**
     * Apply extension to an instance.
     *
     * @param object $instance
     * @return \Pattern\Extension\ExtensionWrapper
     */
    public static function apply($instance)
    {
        return new ExtensionWrapper($instance, \get_called_class());
    }

    /**
     * @param mixed $instance
     * @return boolean
     */
    public static function isExtensible($instance)
    {
        return ($instance instanceof Extensible);
    }
}
?>

<?php

namespace Pattern\Extension;

/**
 * Demarcate decorators that resolve the extension.
 */
interface Extensible
{
    /**
     * Verify the instance of the holded object.
     *
     * @param string $className
     * @return bool true if the instance is of the type $className, false otherwise.
     */
    public function holdsInstanceOf($className);

    /**
     * Returns the wrapped object.
     * If the wrapped object is a Extensible the returns the unwrap of it and so on.
     *
     * @return mixed
     */
    public function unwrap();

    /**
     * Magic method for the extension methods.
     *
     * @param string $name
     * @param array $args
     * @return mixed
     */
    public function __call($name, array $args);
}
?>

<?php

namespace Pattern\Extension;

/**
 * Generic version for the Extensible Interface.
 */
final class ExtensionWrapper implements Extensible
{
    /**
     * @var mixed
     */
    private $that;

    /**
     * @var Extension
     */
    private $extension;

    /**
     * @param object $instance
     * @param string | Extension $extensionClass
     * @throws \InvalidArgumentException
     */
    public function __construct($instance, $extensionClass)
    {
        if (!\is_object($instance)) {
            throw new \InvalidArgumentException('ExtensionWrapper works only with objects.');
        }

        $this->that = $instance;
        $this->extension = $extensionClass;
    }

    /**
     * {@inheritDoc}
     * @see \Pattern\Extension\Extensible::__call()
     */
    public function __call($name, array $args)
    {
        $call = null;
        if (\method_exists($this->extension, '_'.$name)) {
            // this is for abstract default interface implementation
            \array_unshift($args, $this->unwrap());
            $call = array($this->extension, '_'.$name);
        } elseif (\method_exists($this->extension, $name)) {
            // this is for real implementations
            \array_unshift($args, $this->unwrap());
            $call = array($this->extension, $name);
        } else {
            // this is for real call on object
            $call = array($this->that, $name);
        }
        return \call_user_func_array($call, $args);
    }


    /**
     * {@inheritDoc}
     * @see \Pattern\Extension\Extensible::unwrap()
     */
    public function unwrap()
    {
        return (Extension::isExtensible($this->that) ? $this->that->unwrap() : $this->that);
    }

    /**
     * {@inheritDoc}
     * @see \Pattern\Extension\Extensible::holdsInstanceof()
     */
    public function holdsInstanceOf($className)
    {
        return \is_a($this->unwrap(), $className);
    }
}
?>

Basic usage:

1) Create your extension extending from Extension and the static methods;
   class MyExtension extends Extension
   {
      public static function doSomething(ClassToExtend $that)
      {
        // ...
      }
   }

2) Apply extension to the instance you want:

  class ClassToExtend
  {
     public function saySomething()
     {
       // ...
     }
  }
  
  $instance = new ClassToExtend();
  /** @var ClassToExtend|MyExtension $extension */
  $extension = MyExtension::apply($instance);
  
  $extension->saySomething();
  $extension->doSomething();
  
  3) You can add interfaces to Extension Methods but your Extension class must be abstract and a underscore must be in from of the static method.
    <?php
    interface HelloInterfaceExtension
    {
        public function sayHelloFromInterface();
    }
    ?>
    <?php
    use Pattern\Extension\Extension;
    
    abstract class AbstractHelloExtension extends Extension implements HelloInterfaceExtension
    {
        public static function _sayHelloFromInterface(ThirdPartyOrLegacyClass $that)
        {
            return $that->sayHello(). ' from Hello Interface';
        }
    }
    ?>

  4) Use abstract extension methods:
  
    //////////////////////////////////////////
    // Abstract extension
    
    $thatClass = new ThirdPartyHello();
    
    /** @var ThirdPartyHello|HelloInterfaceExtension $extension */
    $extension = AbstractHelloExtension::apply($instance);
    
    $extension->sayHello(); // returns 'Hello'
    $extension->sayHelloFromInterface(); // returns 'Hello from Hello Interface'