PHP手册 - Basic usage

Basic usage

Some simple examples on using the overload() function:

Example #1 Overloading a PHP class


<?php

class OO {
   var $a = 111;
   var $elem = array('b' => 9, 'c' => 42);

   // Callback method for getting a property
   function __get($prop_name, &$prop_value) 
   {
       if (isset($this->elem[$prop_name])) {
           $prop_value = $this->elem[$prop_name];
           return true;
       } else {
           return false;
       }
   }

   // Callback method for setting a property
   function __set($prop_name, $prop_value) 
   {
       $this->elem[$prop_name] = $prop_value;
       return true;
   }
}

// Here we overload the OO object
overload('OO');

$o = new OO;
echo "\$o->a: $o->a\n"; // print: $o->a: 111
echo "\$o->b: $o->b\n"; // print: $o->b: 9
echo "\$o->c: $o->c\n"; // print: $o->c: 42
echo "\$o->d: $o->d\n"; // print: $o->d:

// add a new item to the $elem array in OO
$o->x = 56; 

// instantiate stdclass (it is built-in PHP 4)
// $val is not overloaded!
$val = new stdclass;
$val->prop = 555;

// Set "a" to be an array with the $val object in it
// But __set() will put this in the $elem array
$o->a = array($val);
var_dump($o->a[0]->prop);

?>

PHP手册 - N: Basic usage

用户评论:

Anonymous (26-Jun-2011 09:20)

The result for <?php class Foo{ public function method(){ echo "call Method no paramater"; } public function method($par){ echo "call Method has a paramater"; } } $foo = new Foo(); echo $foo->method("param");] ?> can be achieved by <?php class Foo{ public function method($par = null){ echo "call Method no paramater"; } } $foo = new Foo(); echo $foo->method("param");] ?> Php will give access to both $foo->method() and $foo->method("param")

author at dereleased dot com (21-Dec-2009 08:30)

While the term "overloading" in many other languages specifically means declaring multiple methods with the same name and having the compiler intelligently select which one should be run at any given time, this (as some have pointed out) is not the case in PHP, for a very simple yet important reason: PHP is a weakly/dynamically typed language; the only exceptions to this rule are constants (which have certain type restrictions, e.g. array) and Type-Hinted method arguments. Because of this, traditional overloading style is simply not possible, as there is no way for the interpreter to know which method to call (reliably). However, with PHP's ability to accept an indefinite number of undefined arguments via func_get_args() and related functions, as well as simply provide defaults to values to allow you to declare just one method and perform simple tests to see if some/all of the arguments were indeed passed, traditional means of method overloading are not entirely necessary. It may not be what you're used to, but it works.

scurvysquid at yahoo dot com (04-Jun-2009 03:43)

Overloading is defining a method multiple times with different input parameters, then conditionally running whichever method matches the provided input. It looks like the "overload" function just enables magic methods for a class, which can be used in implementing an extremely janky simulation of overloading. Also, it seems that magic methods are enabled by default in php5 regardless of whether the overload function has been run on a class.

Anonymous (26-Mar-2009 07:48)

You can't redeclare because PHP won't know which one to use. Use a default value and test conditionally instead such as <?php public function method($arg=false){ if($arg==false){ //do something } else { //do something else } } ?>

ly dot sitthykun at yahoo dot com (22-Jan-2009 05:47)

<?php class Foo{ public function method(){ echo "call Method no paramater"; } public function method($par){ echo "call Method has a paramater"; } } $foo = new Foo(); echo $foo->method("param");] ?> #output: Fatal error: Cannot redeclare Foo::method() in class_overload.php on line 6 why? we can not create the same method name.