How can PHP functions and objects be utilized effectively to streamline form validation and input retention processes?

To streamline form validation and input retention processes in PHP, you can create functions to handle validation rules and objects to store and retrieve form data. By encapsulating these processes in functions and objects, you can easily reuse them across multiple forms and pages, making your code more modular and maintainable.

// Function to validate form input
function validateInput($input) {
    // Add your validation rules here
    return $validatedInput;
}

// Object to store form data
class Form {
    private $data = [];

    public function setData($key, $value) {
        $this->data[$key] = $value;
    }

    public function getData($key) {
        return isset($this->data[$key]) ? $this->data[$key] : '';
    }
}

// Example usage
$form = new Form();

if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $username = validateInput($_POST["username"]);
    $email = validateInput($_POST["email"]);

    $form->setData('username', $username);
    $form->setData('email', $email);
}

// Retrieve form data
$usernameValue = $form->getData('username');
$emailValue = $form->getData('email');