Question

When creating a Singleton in PHP, I ensure that it cannot be instantiated by doing the following:

class Singleton {

    private function __construct() {}
    private function __clone() {}

    public static function getInstance() {}
}

However, I realised that defining a class as ‘abstract’ means that it cannot be instantiated. So is there anything wrong with doing the following instead:

abstract class Singleton {

    public static function getInstance() {}
}

The second scenario allows me to write fewer lines of code which would be nice. (Not that it actually makes much of a difference.)

Answer 1

When creating a singleton in PHP, declaring the __construct and __clone as private ensures that the class cannot be instanciated from the outside : it can still be instanciated from inside its declaration.

When declaring a class as abstract, it can not be instanciated at all ; not even from inside its declaration.

This means your solution would not work : in the second case, your getInstance() method will not be able to instanciate the class — while it can do so in the first case.