A concise summary of Magic Method in PHP classes

1. __construct() and __destruct()

are called when the instance is created/destroyed, and can pass 0 or more parameters.

class A
 {
  function A()
  {
   echo "build A";
  }
 
  function __destruct()
  {
   echo "destroy A";
  }
 }
 
 $obj = new A();
 //unset($obj);

Note: The destructor method will be called as soon as there are no other references to a particular object, or in any order during the shutdown sequence.

Regarding constructors, starting from PHP 5.3.3, a method named with the class name in a class defined in a specific namespace will no longer be considered a constructor. In a class without a namespace, it is still a constructor as before. Such as:

namespace Foo;
class Bar {
  public function Bar() {
    // treated as constructor in PHP 5.3.0-5.3.2
    // treated as regular method as of PHP 5.3.3
  }
}

If there is no namespace Foo; then Bar() will also be used as a constructor. In addition, if the following situation exists:

function __construct()
  {
   echo "construct A";
  }
 
  function A()
  {
   echo "build A";
  }
 
  function __destruct()
  {
   echo "destroy A";
  }
 }

contains both __construct() and a function with the same name as the class name, then only __construct( ).

2. __call() and __callStatic()

Called when trying to call a method that does not exist. Two parameters, one is the method name, and the other is the parameter array of the called method.

class MethodTest
{
  public function __call($name, $arguments)
  {
    // Note: value of $name is case sensitive.
    echo "Calling object method '$name' "
       . implode(&#39; &#39;, $arguments). "<br>";
  }
 
  public static function __callStatic($name, $arguments)
  {
    // Note: value of $name is case sensitive.
    echo "Calling static method &#39;$name&#39; "
       . implode(&#39; &#39;, $arguments). "<br>";
  }
}
 
$obj = new MethodTest;
$obj->runTest(&#39;in&#39;,&#39;object&#39;,&#39;context&#39;);
MethodTest::runTest(&#39;in&#39;,&#39;static&#39;,&#39;context&#39;);

Among them, $arguments is passed in as an array. Running results:

Calling object method 'runTest' in object context
Calling static method 'runTest' in static context

Also pay attention to the scope protected and private of the function:

class TestMagicCallMethod {
  public function foo()
  {
    echo __METHOD__.PHP_EOL."<br>";
  }
 
  public function __call($method, $args)
  {
    echo __METHOD__.PHP_EOL."<br>";
    if(method_exists($this, $method))
    {
      $this->$method();
    }
  }
   
  protected function bar()
  {
    echo __METHOD__.PHP_EOL."<br>";
  }
 
  private function baz()
  {
    echo __METHOD__.PHP_EOL."<br>";
  }
}
 
$test  =  new TestMagicCallMethod();
$test->foo();
/**
 * Outputs:
 * TestMagicCallMethod::foo
 */
 
$test->bar();
/**
 * Outputs:
 * TestMagicCallMethod::__call
 * TestMagicCallMethod::bar
 */
 
$test->baz();
/**
 * Outputs:
 * TestMagicCallMethod::__call
 * TestMagicCallMethod::baz
 */

3.__get() and __set()

are called when trying to read properties of an object that do not exist.

Note: We can use this function to implement various operations similar to reflection in java.

class Test
{
  public function __get($key)
  {
   echo $key . " not exists";
  }
  public function __set($key,$value)
  {
   echo $key . " = ".$value;
  }
}
 
$t = new Test();
echo $t->name."<br>";
$t->name = "abc";

Output:
name not exists
name = abc

4. __toString()

This method is similar to Java's toString() method. When we print the object directly, we call this function. The function must return a string.

class Test
{
  private $name = "abc";
  private $age = 12;
 
  public function __toString()
  {
    return "name : $this->name, age : $this->age";
  }
}
 
$t = new Test();
echo $t;

Output:

name: abc, age: 12

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