PHP Magic Constants - PHP Tutorial

PHP provides a set of predefined constants known as “magic constants.” These constants can change their value dynamically based on the context in which they are used. Magic constants are always written with double underscores both at the beginning and the end of their name (except for ClassName::class).

The List of Magic Constants and Their Descriptions

Constant	Description
`__CLASS__`	Outputs the name of the class when used inside a class.
`__DIR__`	Represents the directory path of the current file.
`__FILE__`	Contains the file name including its complete path.
`__FUNCTION__`	Displays the name of the function, if used within one.
`__LINE__`	Indicates the line number where it is called.
`__METHOD__`	Returns the name of the method along with its class.
`__NAMESPACE__`	Displays the namespace name, if used inside a namespace.
`__TRAIT__`	Reflects the name of the trait, if used inside a trait.
`ClassName::class`	Outputs the name of the class, including the namespace, if applicable.

Examples of PHP Magic Constants in Action

Below, we’ll explore examples of how to utilize these magic constants. For added flavor, the variables and identifiers in the examples are inspired by motorcycle and car brands.

Using __CLASS__

class Ducati {
    public function getClassName() {
        return __CLASS__;
    }
}

$motorbike = new Ducati();
echo $motorbike->getClassName(); // Output: Ducati

Using __DIR__

echo "The directory is: " . __DIR__; 
// Output: Displays the directory path of the current file

Using __FILE__

echo "The file path is: " . __FILE__; 
// Output: Displays the full path and file name

Using __FUNCTION__

function harleyFunction() {
    return __FUNCTION__;
}

echo harleyFunction(); // Output: harleyFunction

Using __LINE__

echo "This is line number: " . __LINE__; 
// Output: Displays the current line number in the file

Using __METHOD__

class Toyota {
    public function getMethod() {
        return __METHOD__;
    }
}

$car = new Toyota();
echo $car->getMethod(); // Output: Toyota::getMethod

Using __NAMESPACE__

namespace FordNamespace;

echo __NAMESPACE__; 
// Output: FordNamespace

Using __TRAIT__

trait HondaTrait {
    public function getTraitName() {
        return __TRAIT__;
    }
}

class Sedan {
    use HondaTrait;
}

$vehicle = new Sedan();
echo $vehicle->getTraitName(); // Output: HondaTrait

Using ClassName::class

namespace Lamborghini;

class Aventador {}

echo Aventador::class; 
// Output: Lamborghini\Aventador