Deprecated Widget Constructors

correct-method.php

<?php
/**
 * Correct method for WordPress 4.3
 * @see https://make.wordpress.org/core/2015/07/02/deprecating-php4-style-constructors-in-wordpress-4-3/
 * @see http://codex.wordpress.org/Widgets_API
 */
class My_Widget extends WP_Widget {

	/**
	 * Sets up the widgets name etc
	 */
	public function __construct() {
		$widget_args = array( 'description' => __( 'A Foo Widget', 'text_domain' ) );
		parent::__construct(
			'foo_widget', // Base ID
			__( 'Widget Title', 'text_domain' ), // Name
			$widget_args // Args
		);
	}

	/**
	 * Outputs the content of the widget
	 *
	 * @param array $args
	 * @param array $instance
	 */
	public function widget( $args, $instance ) {
		// outputs the content of the widget
	}

	/**
	 * Outputs the options form on admin
	 *
	 * @param array $instance The widget options
	 */
	public function form( $instance ) {
		// outputs the options form on admin
	}

	/**
	 * Processing widget options on save
	 *
	 * @param array $new_instance The new options
	 * @param array $old_instance The previous options
	 */
	public function update( $new_instance, $old_instance ) {
		// processes widget options to be saved
	}
}

deprecated-method.php

<?php
/**
 * Deprecated Method as of WordPress 4.3
 * @see https://make.wordpress.org/core/2015/07/02/deprecating-php4-style-constructors-in-wordpress-4-3/
 * @see http://codex.wordpress.org/Widgets_API
 */
class My_Widget extends WP_Widget {

	/**
	 * Sets up the widgets name etc
	 */
	public function My_Widget() {
		$widget_args = array( 'description' => __( 'A Foo Widget', 'text_domain' ) );
		$this->WP_Widget(
			'foo_widget', // Base ID
			__( 'Widget Title', 'text_domain' ), // Name
			$widget_args // Args
		);
	}

	/**
	 * Outputs the content of the widget
	 *
	 * @param array $args
	 * @param array $instance
	 */
	public function widget( $args, $instance ) {
		// outputs the content of the widget
	}

	/**
	 * Outputs the options form on admin
	 *
	 * @param array $instance The widget options
	 */
	public function form( $instance ) {
		// outputs the options form on admin
	}

	/**
	 * Processing widget options on save
	 *
	 * @param array $new_instance The new options
	 * @param array $old_instance The previous options
	 */
	public function update( $new_instance, $old_instance ) {
		// processes widget options to be saved
	}
}