Singleton Pattern for functions.php

DashboardWidget.php

<?php namespace CharityPress\Functions;

/**
 * Enqueue scripts and styles.
 */
class DashboardWidget extends Singleton {

	//required function
	public function init() {
		add_action( 'wp_dashboard_setup', [ $this, 'intro_widget' ] );
	}

	public function intro_widget() {
		wp_add_dashboard_widget( 'custom_help_widget', 'Theme Introduction', 'intro_widget_output' );
	}

	public function intro_widget_output() {
		echo '<p>Welcome to Charity Press! Need help? Contact the developers <a href="mailto:info@reasondigital.com">here</a>.</p>';
	}

}

functions.php

<?php

require "vendor/autoload.php";

CharityPress\Functions\DashboardWidget::get_instance();