Recap: Review where we left off last time.

https://github.com/dinocajic/php-youtube-tutorials/tree/master

https://blog.devgenius.io/php-p70-sub-namespaces-11ff9c0f0787

Magic constants aren’t complicated. The best way to illustrate them is through an example. Lets make a modification to our get_year_make_and_model() method inside of our Car class and start including some of these magic constants to see what they do.

<?php
namespace Vehicles\Cars;

//...

class Car extends \Vehicles\Vehicle
{
    //...

    public function get_year_make_and_model(): string
    {
        return $this->year . " " . $this->make . " " . $this->model;
    }
}

First one we’ll look at is the __LINE__ magic constant.

<?php
namespace Vehicles\Cars;

//...

class Car extends \Vehicles\Vehicle
{
    //...

    public function get_year_make_and_model(): string
    {
        return $this->year . " " . $this->make . " " . $this->model . "<br>" .
            "Line #: " . __LINE__ . "<br>";
    }
}

What do you think that we get? That’s right. It’s the current line in the code. In this case, it would be “Line #: 13” since that’s the line of code that contains the __LINE__ magic constant.

<?php
namespace Vehicles\Cars;

//...

class Car extends \Vehicles\Vehicle
{
    //...

    public function get_year_make_and_model(): string
    {
        return $this->year . " " . $this->make . " " . $this->model . "<br>" .
            "Line #: " . __LINE__ . "<br>" .
            "File: "   . __FILE__ . "<br>";
    }
}

The __FILE__ magic constant returns the absolute file path where the __FILE__ magic constant was inserted. For me, it’s C:/www/youtube/php/71_Magic_Constants/Car.php.

<?php
namespace Vehicles\Cars;

//...

class Car extends \Vehicles\Vehicle
{
    //...

    public function get_year_make_and_model(): string
    {
        return $this->year . " " . $this->make . " " . $this->model . "<br>" .
            "Line #: " . __LINE__ . "<br>" .
            "File: "   . __FILE__ . "<br>" .
            "Directory: " . __DIR__ . "<br>";
    }
}

The __DIR__ magic constant provides us with the directory of the file that contains the __DIR__ magic constant. It’s nearly identical to the __FILE__, but does not include the file name itself.

C:/www/youtube/php/71_Magic_Constants

<?php
namespace Vehicles\Cars;

//...

class Car extends \Vehicles\Vehicle
{
    //...

    public function get_year_make_and_model(): string
    {
        return $this->year . " " . $this->make . " " . $this->model . "<br>" .
            "Line #: " . __LINE__ . "<br>" .
            "File: "   . __FILE__ . "<br>" .
            "Directory: " . __DIR__ . "<br>" .
            "Class: " . __CLASS__ . "<br>";
    }
}

The __CLASS__ returns the class name that contains the __CLASS__ magic constant, which is Vehicles\Cars\Car. It gives you the full name-spaced output so that you know which class it’s actually referencing.

I think you’re starting to get the picture. If we call the __METHOD__ and the __ NAMESPACE__ magic constants, they’re going to return the method and the namespace that contain these magic constants, in this case Vehicles\Cars\Car::get_year_make_and_model and Vehicles\Cars.

<?php
namespace Vehicles\Cars;

//...

class Car extends \Vehicles\Vehicle
{
    //...

    public function get_year_make_and_model(): string
    {
        return $this->year . " " . $this->make . " " . $this->model . "<br>" .
            "Line #: " . __LINE__ . "<br>" .
            "File: "   . __FILE__ . "<br>" .
            "Directory: " . __DIR__ . "<br>" .
            "Class: " . __CLASS__ . "<br>" .
            "Method: " . __METHOD__ . "<br>" .
            "Namespace: " . __NAMESPACE__. "<br>";
    }
}

The only one that we haven’t looked at is the __TRAIT__. If we placed this in the same code, we’re not going to get anything, since this class is not a trait. However, we do have traits, such as the Engine trait where we can make a modification to its method, check_oil_level.

<?php
namespace Vehicles\Cars\CarParts;

trait Engine {

    public function check_oil_level() {
        echo "Engine oil level good. Trait: " . __TRAIT__;
    }
}

If we call the above code, we get Vehicles/Cars/CarParts/Engine as the output.

That’s it. I told you that it would be nice and simple. Most of the time you would use them in your log files so that you can point to errors quickly.