What is a latch?

Coupling is the degree of dependence between modules or components of a program. The stronger the coupling, the more tightly connected the modules are, and changes in one can affect the other. In object-oriented programming, the goal is to achieve loose coupling to improve maintainability and flexibility of the code.

For example, if class A directly uses the internal details of class B, this is strong coupling. To reduce coupling, interfaces, abstractions, or dependency injection are used.

An example of loose coupling in PHP:

interface LoggerInterface {
    public function log(string $message);
}

class FileLogger implements LoggerInterface {
    public function log(string $message) {
        // write to file
    }
}

class UserService {
    private LoggerInterface $logger;

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

    public function createUser() {
        // create user
        $this->logger->log('User created');
    }
}

Here, UserService depends on the abstraction LoggerInterface, not on a specific implementation, which reduces coupling.