PHP 7.0 - Anonymous Classes

A new feature of php 7.0 is anonymous classes. Anonymous classes are useful when simple, one-off objects need to be created, such as a value object. Below is an example of using an anonymous class for ensuring a user provided string is valid, and converts it for later use.

// set a value for this example, but imagine the user 
// was posting this in a form.
$_POST['var1'] = 'another_type'; 

$valueObj = new class($_POST['var1']) {
    private $m_value;

    public function __construct(string $input)
    {
        switch ($input)
        {
            case 'type1' : $this->m_value = 1; break;
            case 'type2' : $this->m_value = 2; break;
            case 'another_type' : $this->m_value = 3; break;
            default : throw new Exception("Invalid input: $input");
        }
    }

    public function getValue() : int { return $this->m_value; }
};

print $valueObj->getValue(); // 3

Remember that you have created an object, rather than a class definition, so you couldn't do this:

$myOtherObj = new $valueObj('type2);

Another possible use for anonymous classes is to create a one off object that implements an interface for dependency injection rather than having to create a whole new class file somewhere. E.g.

interface Logger 
{
    public function log(string $input);
}

class MyClassThatRequiresALogger
{
    private $m_logger;

    public function __construct(Logger $logger)
    {
        $this->m_logger = $logger;
    }

    public function run()
    {
        // do something here...
        $this->m_logger->log("I did something!");
    }
}

$logger = new class()  implements Logger {
    public function log(string $input) { print($input); }
};

$myClass = new MyClassThatRequiresALogger($logger);
$myClass->run(); // I did something!