add search to menu in wordpress via functions

add search to menu.php

<?php
/**
 * ANCHOR Add search box to primary menu
 */
function elab_nav_search($items, $args) {
    // If this isn't the primary menu, do nothing
    if ( !($args->theme_location == 'primary') ) :
		return $items;
	endif;
    // Otherwise, add search form
    return $items . '<li class="search-form">' . get_search_form(false) . '</li>';
}
add_filter('wp_nav_menu_items', 'elab_nav_search', 10, 2);