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IndietroCapitolo 14. Classes and Objects (PHP 5)Avanti

Reflection

Introduction

PHP 5 comes with a complete reflection API that adds the ability to reverse-engineer classes, interfaces, functions and methods as well as extensions. Additionally, the reflection API also offers ways of retrieving doc comments for functions, classes and methods.

The reflection API is an object-oriented extension to the Zend Engine, consisting of the following classes:

<?php
  class Reflection { }
  interface Reflector { }
  class ReflectionException extends Exception { }
  class ReflectionFunction implements Reflector { }
  class ReflectionParameter implements Reflector { }
  class ReflectionMethod extends ReflectionFunction { }
  class ReflectionClass implements Reflector { }
  class ReflectionObject extends ReflectionClass { }
  class ReflectionProperty implements Reflector { }
  class ReflectionExtension implements Reflector { }
?>

Nota: For details on these classes, have a look at the next chapters.

If we were to execute the code in the example below:

Esempio 14-7. Basic usage of the reflection API

<?php
  Reflection::export(new ReflectionClass('Exception'));
?>
We will see: 
Class [ <internal> class Exception ] {

  - Constants [0] {
  }

  - Static properties [0] {
  }

  - Static methods [0] {
  }

  - Properties [6] {
    Property [ <default> protected $message ]
    Property [ <default> private $string ]
    Property [ <default> protected $code ]
    Property [ <default> protected $file ]
    Property [ <default> protected $line ]
    Property [ <default> private $trace ]
  }

  - Methods [9] {
    Method [ <internal> final private method __clone ] {
    }

    Method [ <internal> <ctor> method __construct ] {
    }

    Method [ <internal> final public method getMessage ] {
    }

    Method [ <internal> final public method getCode ] {
    }

    Method [ <internal> final public method getFile ] {
    }

    Method [ <internal> final public method getLine ] {
    }

    Method [ <internal> final public method getTrace ] {
    }

    Method [ <internal> final public method getTraceAsString ] {
    }

    Method [ <internal> public method __toString ] {
    }
  }
}

ReflectionFunction

The ReflectionFunction class lets you reverse-engineer functions.

<?php
  class ReflectionFunction implements Reflector {
      public object __construct(string name)
      public string __toString()
      public static string export()
      public string getName()
      public bool isInternal()
      public bool isUserDefined()
      public string getFileName()
      public int getStartLine()
      public int getEndLine()
      public string getDocComment()
      public array getStaticVariables()
      public mixed invoke(mixed* args)
      public bool returnsReference()
      public ReflectionParameter[] getParameters()
  }
?>

To introspect a function, you will first have to create an instance of the ReflectionFunction class. You can then call any of the above methods on this instance.

Esempio 14-8. Using the ReflectionFunction class

<?php
/**
* A simple counter
*
* @return    int
*/
function counter()
{
    static $c = 0;

    return $c++;
}

// Create an instance of the Reflection_Function class
$func = new ReflectionFunction('counter');

// Print out basic information
printf(
    "===> The %s function '%s'\n".
    "     declared in %s\n".
    "     lines %d to %d\n",
    $func->isInternal() ? 'internal' : 'user-defined',
    $func->getName(),
    $func->getFileName(),
    $func->getStartLine(),
    $func->getEndline()
);

// Print documentation comment
printf("---> Documentation:\n %s\n", var_export($func->getDocComment(), 1));

// Print static variables if existant
if ($statics = $func->getStaticVariables())
{
    printf("---> Static variables: %s\n", var_export($statics, 1));
}

// Invoke the function
printf("---> Invokation results in: ");
var_dump($func->invoke());


// you may prefer to use the export() method
echo "\nReflectionFunction::export() results:\n";
echo ReflectionFunction::export('counter');
?>

Nota: The method invoke() accepts a variable number of arguments which are passed to the function just as in call_user_func().

ReflectionParameter

The ReflectionParameter class retrieves information about a function's or method's parameters.

<?php
  class ReflectionParameter implements Reflector {
      public object __construct(string name)
      public string __toString()
      public static string export()
      public string getName()
      public ReflectionClass getClass()
      public bool allowsNull()
      public bool isPassedByReference()
  }
?>

To introspect function parameters, you will first have to create an instance of the ReflectionFunction or ReflectionMethod classes and then use their getParameters() method to retrieve an array of parameters.

Esempio 14-9. Using the ReflectionParameter class

<?php
    function foo($a, $b, $c) { }
    function bar(Exception $a, &$b, $c) { }
    function baz($a = 1, $b = NULL, ReflectionFunction $c) { }
    function abc() { }

    // Create an instance of Reflection_Function with the
    // parameter given from the command line.    
    $reflect = new ReflectionFunction($argv[1]);

    echo $reflect;

    foreach ($reflect->getParameters() as $i => $param)
    {
        printf(
            "-- Parameter #%d: %s {\n".
            "   Class: %s\n".
            "   Allows NULL: %s\n".
            "   Passed to by reference: %s\n".
            "}\n",
            $i,
            $param->getName(),
            var_export($param->getClass(), 1),
            var_export($param->allowsNull(), 1),
            var_export($param->isPassedByReference(), 1)
        );
    }
?>

ReflectionClass

The ReflectionClass class lets you reverse-engineer classes.

<?php
  class ReflectionClass implements Reflector {
      public __construct(string name)
      public string __toString()
      public static string export()
      public string getName()
      public bool isInternal()
      public bool isUserDefined()
      public string getFileName()
      public int getStartLine()
      public int getEndLine()
      public string getDocComment()
      public ReflectionMethod getConstructor()
      public ReflectionMethod getMethod(string name)
      public ReflectionMethod[] getMethods()
      public ReflectionProperty getProperty(string name)
      public ReflectionProperty[] getProperties()
      public array getConstants()
      public mixed getConstant(string name)
      public bool isInstantiable()
      public bool isInterface()
      public bool isFinal()
      public bool isAbstract()
      public int getModifiers()
      public bool isInstance(stdclass object)
      public stdclass newInstance(mixed* args)
      public ReflectionClass[] getInterfaces()
      public ReflectionClass getParentClass()
      public bool isSubclassOf(ReflectionClass class)
  }
?>

To introspect a class, you will first have to create an instance of the ReflectionClass class. You can then call any of the above methods on this instance.

Esempio 14-10. Using the ReflectionClass class

<?php
  interface Serializable
  {
      // ...
  }

  class Object
  {
      // ...
  }

  /**
   * A counter class
   *
   */
  class Counter extends Object implements Serializable
  {
      const START = 0;
      private static $c = Counter::START;

      /**
       * Invoke counter
       *
       * @access  public
       * @return  int
       */
      public function count()
      {
          return self::$c++;
      }
  }

  // Create an instance of the ReflectionClass class
  $class= new ReflectionClass('Counter');

  // Print out basic information
  printf(
      "===> The %s%s%s %s '%s' [extends %s]\n".
      "     declared in %s\n".
      "     lines %d to %d\n".
      "     having the modifiers %d [%s]\n",
      $class->isInternal() ? 'internal' : 'user-defined',
      $class->isAbstract() ? ' abstract' : '',
      $class->isFinal() ? ' final' : '',
      $class->isInterface() ? 'interface' : 'class',
      $class->getName(),
      var_export($class->getParentClass(), 1),
      $class->getFileName(),
      $class->getStartLine(),
      $class->getEndline(),
      $class->getModifiers(),
      implode(' ', Reflection::getModifierNames($class->getModifiers()))
  );

  // Print documentation comment
  printf("---> Documentation:\n %s\n", var_export($class->getDocComment(), 1));

  // Print which interfaces are implemented by this class
  printf("---> Implements:\n %s\n", var_export($class->getInterfaces(), 1));

  // Print class constants
  printf("---> Constants: %s\n", var_export($class->getConstants(), 1));

  // Print class properties
  printf("---> Properties: %s\n", var_export($class->getProperties(), 1));

  // Print class methods
  printf("---> Methods: %s\n", var_export($class->getMethods(), 1));

  // If this class is instantiable, create an instance
  if ($class->isInstantiable())
  {
      $counter= $class->newInstance();

      echo '---> $counter is instance? ';
      echo $class->isInstance($counter) ? 'yes' : 'no';

      echo "\n---> new Object() is instance? ";
      echo $class->isInstance(new Object()) ? 'yes' : 'no';
  }
?>

Nota: The method newInstance() accepts a variable number of arguments which are passed to the function just as in call_user_func().

Nota: $class = new ReflectionClass('Foo'); $class->isInstance($arg) is equivalent to $arg instanceof Foo or is_a($arg, 'Foo').

ReflectionMethod

The ReflectionMethod class lets you reverse-engineer class methods.

<?php
  class ReflectionMethod extends ReflectionFunction {
      public __construct(mixed class, string name)
      public static string export()
      public mixed invoke(stdclass object, mixed* args)
      public bool isFinal()
      public bool isAbstract()
      public bool isPublic()
      public bool isPrivate()
      public bool isProtected()
      public bool isStatic()
      public bool isConstructor()
      public int getModifiers()
      public ReflectionClass getDeclaringClass()

      /* Inherited from ReflectionFunction */
      public string __toString()
      public string getName()
      public bool isInternal()
      public bool isUserDefined()
      public string getFileName()
      public int getStartLine()
      public int getEndLine()
      public string getDocComment()
      public array getStaticVariables()
      public bool returnsReference()
      public ReflectionParameter[] getParameters()
  }
?>

To introspect a method, you will first have to create an instance of the ReflectionMethod class. You can then call any of the above methods on this instance.

Esempio 14-11. Using the ReflectionMethod class

<?php
  class Counter {
      private static $c = 0;

      /**
       * Increment counter
       *
       * @final
       * @static
       * @access  public
       * @return  int
       */
      final public static function increment()
      {
          self::$c++;
          return self::$c;
      }
  }

  // Create an instance of the Reflection_Method class
  $method= new ReflectionMethod('Counter', 'increment');

  // Print out basic information
  printf(
    "===> The %s%s%s%s%s%s%s method '%s' (which is %s)\n".
    "     declared in %s\n".
    "     lines %d to %d\n".
    "     having the modifiers %d[%s]\n",
    $method->isInternal() ? 'internal' : 'user-defined',
    $method->isAbstract() ? ' abstract' : '',
    $method->isFinal() ? ' final' : '',
    $method->isPublic() ? ' public' : '',
    $method->isPrivate() ? ' private' : '',
    $method->isProtected() ? ' protected' : '',
    $method->isStatic() ? ' static' : '',
    $method->getName(),
    $method->isConstructor() ? 'the constructor' : 'a regular method',
    $method->getFileName(),
    $method->getStartLine(),
    $method->getEndline(),
    $method->getModifiers(),
    implode(' ', Reflection::getModifierNames($method->getModifiers()))
  );

  // Print documentation comment
  printf("---> Documentation:\n %s\n", var_export($method->getDocComment(), 1));

  // Print static variables if existant
  if ($statics= $method->getStaticVariables())
  {
      printf("---> Static variables: %s\n", var_export($statics, 1));
  }

  // Invoke the method
  printf("---> Invokation results in: ");
  var_dump($method->invoke(NULL));
?>

Nota: Trying to invoke private, protected or abstract methods will result in an exception being thrown from the invoke() method.

Nota: For static methods as seen above, you should pass NULL as the first argument to invoke(). For non-static methods, pass an instance of the class.

ReflectionProperty

The ReflectionProperty class lets you reverse-engineer class properties.

<?php
  class ReflectionProperty implements Reflector {
      public __construct(mixed class, string name)
      public string __toString()
      public static string export()
      public string getName()
      public bool isPublic()
      public bool isPrivate()
      public bool isProtected()
      public bool isStatic()
      public bool isDefault()
      public int getModifiers()
      public mixed getValue(stdclass object)
      public void setValue(stdclass object, mixed value)
      public ReflectionClass getDeclaringClass()
  }
?>

To introspect a method, you will first have to create an instance of the ReflectionProperty class. You can then call any of the above methods on this instance.

Esempio 14-12. Using the ReflectionProperty class

<?php
  class String
  {
      public $length  = 5;
  }

  // Create an instance of the ReflectionProperty class
  $prop = new ReflectionProperty('String', 'length');

  // Print out basic information
  printf(
      "===> The%s%s%s%s property '%s' (which was %s)\n".
      "     having the modifiers %s\n",
      $prop->isPublic() ? ' public' : '',
      $prop->isPrivate() ? ' private' : '',
      $prop->isProtected() ? ' protected' : '',
      $prop->isStatic() ? ' static' : '',
      $prop->getName(),
      $prop->isDefault() ? 'declared at compile-time' : 'created at run-time',
      var_export(Reflection::getModifierNames($prop->getModifiers()), 1)
  );

  // Create an instance of String
  $obj= new String();

  // Get current value
  printf("---> Value is: ");
  var_dump($prop->getValue($obj));

  // Change value
  $prop->setValue($obj, 10);
  printf("---> Setting value to 10, new value is: ");
  var_dump($prop->getValue($obj));

  // Dump object
  var_dump($obj);
?>

Nota: Trying to get or set private or protected class property's values will result in an exception being thrown.

ReflectionExtension

The ReflectionExtension class lets you reverse-engineer extensions. You can retrieve all loaded extensions at runtime using the get_loaded_extensions().

<?php
  class ReflectionExtension implements Reflector {
      public __construct(string name)
      public string __toString()
      public static string export()
      public string getName()
      public string getVersion()
      public ReflectionFunction[] getFunctions()
      public array getConstants()
      public array getINIEntries()
  }
?>

To introspect a method, you will first have to create an instance of the ReflectionProperty class. You can then call any of the above methods on this instance.

Esempio 14-13. Using the ReflectionExtension class

<?php
  // Create an instance of the ReflectionProperty class
  $ext = new ReflectionExtension('standard');

  // Print out basic information
  printf(
      "Name        : %s\n".
      "Version     : %s\n".
      "Functions   : [%d] %s\n".
      "Constants   : [%d] %s\n".
      "INI entries : [%d] %s\n",
      $ext->getName(),
      $ext->getVersion() ? $ext->getVersion() : 'NO_VERSION',
      sizeof($ext->getFunctions()),
      var_export($ext->getFunctions(), 1),
      sizeof($ext->getConstants()),
      var_export($ext->getConstants(), 1),
      sizeof($ext->getINIEntries()),
      var_export($ext->getINIEntries(), 1)
  );
?>

Extending the reflection classes

In case you want to create specialized versions of the built-in classes (say, for creating colorized HTML when being exported, having easy-access member variables instead of methods or having utility methods), you may go ahead and extend them.

Esempio 14-14. Extending the built-in classes

<?php
  /**
   * My Reflection_Method class
   *
   */
  class My_Reflection_Method extends ReflectionMethod {
    public $visibility= '';

    public function __construct($o, $m) {
      parent::__construct($o, $m);
      $this->visibility= Reflection::getModifierNames($this->getModifiers());
    }
  }

  /**
   * Demo class #1
   *
   */
  class T {
    protected function x() {}
  }

  /**
   * Demo class #2
   *
   */
  class U extends T {
    function x() {}
  }

  // Print out information
  var_dump(new My_Reflection_Method('U', 'x'));
?>

Nota: Caution: If you're overwriting the constructor, remember to call the parent's constructor _before_ any code you insert. Failing to do so will result in the following: Fatal error: Internal error: Failed to retrieve the reflection object

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