there are eight magical constant that changes depanding on where they are used. here are all magic constant is described

PHP Magic Constant

<?php
/*there are eight magical constant that changes depanding on where they are used
__LINE__	The current line number of the file.

__FILE__	The full path and filename of the file with symlinks resolved. If used inside an include, the name of the included file is returned.

__DIR__	The directory of the file. If used inside an include, the directory of the included file is returned. This is equivalent to dirname(__FILE__). This directory name does not have a trailing slash unless it is the root directory.

__FUNCTION__	The function name.

__CLASS__	The class name. The class name includes the namespace it was declared in (e.g. Foo\Bar). Note that as of PHP 5.4 __CLASS__ works also in traits. When used in a trait method, __CLASS__ is the name of the class the trait is used in.

__TRAIT__	The trait name. The trait name includes the namespace it was declared in (e.g. Foo\Bar).

__METHOD__	The class method name.

__NAMESPACE__	The name of the current namespace.
*/


class trick{
	public function doit(){
		echo __FUNCTION__;
	}
	public function doitagain(){
		echo __METHOD__;
	}
}

$obj1 = new trick();
$obj1->doit();
echo '<br>';
$obj1->doitagain();
echo '<br>';
echo '<br>';
function testFunction(){
	echo '<br>'.__FUNCTION__;
	echo '<br>'.__FILE__;
	echo '<br>'.__DIR__;
	echo '<br>'.dirname(__FILE__);
}
testFunction();

echo '<br>';
echo '<br>';
//the __CLASS__ magic constant nicely complements the get_class() function
class baseClass{
	function say_a(){
		echo " 'a' - Said the ". __CLASS__ . "<br>";
	}
	function say_b(){
		echo " 'b' - Said the ". get_class($this) . "<br>";
	}
}
class subClass extends baseClass{
	function say_a(){
		parent::say_a();
		echo " 'a' - Said the ". __CLASS__ . "<br>";
	}
	function say_b(){
		parent::say_b();
		echo " 'b' - Said the ". get_class($this) . "<br>";
	}
}

$obj = new subClass();
$obj->say_a();
$obj->say_b();