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Magic Functions

Magic functions are functions that are triggered automatically when special events happen. They can be defined in any class.

__construct([$m1,$m2……]) is called when an object is created. A child class can override the parent’s ‘constructor’ with a different arguments signature. $m1, $m2 can be any content type (mixed). __destruct() is called when there are no more references to an object. __clone() is called when an object is cloned.
The destructor is called before the script ends.
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<!DOCTYPE html>
<html>
<head></head>
<body><?php

class C{
   function __construct($s){ echo "Constructor".$s;}
   function __destruct(){ echo "Destructor called. ";}
   function __clone(){ echo "__clone() called. ";}
}

$a=new C(" called. ");  // Constructor called.
$b=clone $a;               // __clone() called.
$a=$b;                       // Destructor called.
$c=clone $a;               // __clone called().

?></body>
</html>
__set($s,$m) is called when writing data to undeclared properties. __get($s) is called when reading data from undeclared properties. It can return any type. __isset($s) is triggered by calling isset() or empty() on undeclared properties. It returns a boolean value. __unset($s) is triggered when unset() is used on undeclared properties.

__call($s,$arr) is called when invoking undeclared methods in an object context. It can return any type. __callStatic($s,$arr) is triggered when invoking undeclared methods in a static context. It can return any type. __invoke ([$m1,$m2……]) is called when a script tries to call an object as a function. It can return any type.

__toString() is called when the object is treated like a string. It returns a string.
The destructor is called before the script ends.
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<!DOCTYPE html>
<html>
<head></head>
<body><?php

class C{
   function __set($name,$value){
      echo "Trying to set \$$name to $value...<br />";
   }
   function __get($name){
      echo "Trying to get a value from \$$name...<br />";
      return 5;
   }
   function __isset($name){
      echo "Checking if \$$name is set...<br />";
      return true;
   }
   function __unset($name){
      echo "Trying to unset \$$name...<br />";
   }
   function __call($name,$arr){
      echo "Trying to call $name() with $arr[0]...<br />";
   }
   static function __callStatic($name,$arr){
      echo "Trying to call $name() statically with $arr[0]...<br />";
   }
   function __invoke($s){
      echo "Trying to invoke a function with $s...<br />";
   }
   function __toString(){
      return "Trying to be treated like a string...<br />";
   }
}
$a=new C;  // $a->x is an undeclared property
$a->x=5;
$b=$a->x;
$c=isset($a->x);
unset($a->x);
$a->x("TEST");
$a::x("TEST");
$a("TEST");
echo $a;
?></body>
</html>