Master PHP Magic Constants: __FUNCTION__, __METHOD__, __CLASS__, ::class and More

Overview

PHP defines nine magic constants that are resolved at compile time, unlike user‑defined constants. Their values depend on where they are used in the code.

__FUNCTION__

The __FUNCTION__ constant returns the name of the function or method in which it appears; outside a function it yields an empty string.

Using in a function

function myFunction(){
    echo __FUNCTION__;
}

Calling myFunction() prints myFunction.

Using in a class method

class MyClass{
    public function myMethod(){
        echo __FUNCTION__;
    }
}

Calling (new MyClass())->myMethod() prints myMethod.

Using in an anonymous function

$myFunction = function(){
    echo __FUNCTION__;
};

Invoking $myFunction() outputs {closure}.

__METHOD__

The __METHOD__ constant returns the fully qualified class name and method name when used inside a method; otherwise it behaves like __FUNCTION__.

In a class method

namespace App\Utilities;
class MyClass{
    public function myMethod(){
        echo __METHOD__;
    }
}

Calling (new MyClass())->myMethod() prints App\Utilities\MyClass::myMethod.

In a parent class method

namespace App\Utilities;
class ParentClass{
    public function myMethod(){
        echo __METHOD__;
    }
}
class ChildClass extends ParentClass{}

Calling (new ChildClass())->myMethod() prints App\Utilities\ParentClass::myMethod.

In a function

Inside a plain function, __METHOD__ outputs the same as __FUNCTION__ – the function name.

__CLASS__

The __CLASS__ constant returns the name of the class where it is used; outside a class it returns an empty string.

In a class method

namespace App\Utilities;
class MyClass{
    public function myMethod(){
        echo __CLASS__;
    }
}

Calling (new MyClass())->myMethod() prints MyClass.

In a parent class

When used in a parent class, __CLASS__ always returns the parent’s name, even when called from a child.

In a trait

namespace App\Utilities;
trait MyTrait{
    public function myMethod(){
        echo __CLASS__;
    }
}
class MyClass{ use MyTrait; }

Calling (new MyClass())->myMethod() prints App\Utilities\MyClass.

::class

The ::class constant yields the fully qualified class name as a string, which is especially handy in Laravel for route definitions and model relationships.

Laravel route example

use App\Http\Controllers\UserController;
Route::get('/users', [UserController::class, 'index']);

Laravel model relationship example

namespace App\Models;
use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\Relations\HasMany;
class User extends Model{
    public function posts(): HasMany{
        return $this->hasMany(Post::class);
    }
}

__TRAIT__

The __TRAIT__ constant returns the fully qualified name of the trait where it is used; outside a trait it returns an empty string.

namespace App\Utilities;
trait MyTrait{
    public function myMethod(){
        echo __TRAIT__;
    }
}
class MyClass{ use MyTrait; }

Calling (new MyClass())->myMethod() prints App\Utilities\MyTrait.

__NAMESPACE__

The __NAMESPACE__ constant returns the current namespace of the file; if the file has no namespace, it returns an empty string.

namespace App\Utilities;
echo __NAMESPACE__;

This outputs App\Utilities.

__LINE__

The __LINE__ constant returns the line number where it appears in the source file.

<?php
// An empty line...

echo __LINE__;

The above script prints 5 because the echo statement is on line 5.

__FILE__

The __FILE__ constant returns the full path and filename of the file in which it is used.

echo __FILE__;

If the script resides at /Users/ashleyallen/my-app/index.php, the output is that full path.

__DIR__

The __DIR__ constant returns the directory of the file. It does not include a trailing slash unless the directory is the root.

echo __DIR__;

Running the example in /Users/ashleyallen/my-app/index.php prints /Users/ashleyallen/my-app. The same value can be obtained with dirname(__FILE__).