PHP: Abstract method within an interface

Question

why cannot I declare an abstract method within an interface? This is my code. Thank you.

<?php
interface Connection {
    public abstract function connect();
    public function getConnection();
}

abstract class ConnectionAbstract implements Connection() {
    private $connection;

    public abstract function connect();

    public function getConnection() {
        return $this->connection;
    }
}

class MySQLConnection extends ConnectionAbstract {
    public function connect() {
        echo 'connecting ...';
    }
}

$c = new MySQLConnection();
?>

Answer 1

All functions in an interface are implicitly abstract. There is no need to use the abstract keyword when declaring the function.

Answer 2

Remember that the requirement of a class which implements an interface must contain a series of public methods which correspond to the method signatures declared in the interface. So, for instance, when you declare an interface which has a defined public abstract function, you're literally saying that every class which implements the interface must have a public abstract method named connect. Since objects with abstract methods cannot be instantiated, you'll end up writing an interface which can never be used.