PHP walker class arrays and objects

I am working with the walker class to create a menu for a WordPress theme and the code I have is;

class Walker_Nav_Primary extends Walker_Nav_menu {

    function start_lvl( &$output, $depth = 0, $args = array() ){ //ul
        $indent = str_repeat("t",$depth);
        $submenu = ($depth > 0) ? ' sub-menu' : '';
        $output .= "n$indent<ul class="dropdown-menu$submenu depth_$depth">n";
    }

    function start_el( &$output, $item, $depth = 0, $args = array(), $id = 0 ){ //li a span

        $indent = ( $depth ) ? str_repeat("t",$depth) : '';

        $li_attributes = '';
        $class_names = $value = '';

        $classes = empty( $item->classes ) ? array() : (array) $item->classes;

        $classes[] = ($args->walker->has_children) ? 'dropdown' : '';
        $classes[] = ($item->current || $item->current_item_ancestor) ? 'active' : '';
        $classes[] = 'menu-item-' . $item->ID;
        if( $depth && $args->walker->has_children ){
            $classes[] = 'dropdown-submenu';
        }

        $class_names =  join(' ', apply_filters('nav_menu_css_class', array_filter( $classes ), $item, $args ) );
        $class_names = ' class="' . esc_attr($class_names) . '"';

        $id = apply_filters('nav_menu_item_id', 'menu-item-'.$item->ID, $item, $args);
        $id = strlen( $id ) ? ' id="' . esc_attr( $id ) . '"' : '';

        $output .= $indent . '<li' . $id . $value . $class_names . $li_attributes . '>';

        $attributes = ! empty( $item->attr_title ) ? ' title="' . esc_attr($item->attr_title) . '"' : '';
        $attributes .= ! empty( $item->target ) ? ' target="' . esc_attr($item->target) . '"' : '';
        $attributes .= ! empty( $item->xfn ) ? ' rel="' . esc_attr($item->xfn) . '"' : '';
        $attributes .= ! empty( $item->url ) ? ' href="' . esc_attr($item->url) . '"' : '';

        $attributes .= ( $args->walker->has_children ) ? ' class="dropdown-toggle" data-toggle="dropdown"' : '';

        $item_output = $args->before;
        $item_output .= '<a' . $attributes . '>';
        $item_output .= $args->link_before . apply_filters( 'the_title', $item->title, $item->ID ) . $args->link_after;
        $item_output .= ( $depth == 0 && $args->walker->has_children ) ? ' <b class="caret"></b></a>' : '</a>';
        $item_output .= $args->after;

        $output .= apply_filters ( 'walker_nav_menu_start_el', $item_output, $item, $depth, $args );

    }

}

However, when a friend viewed the theme he was seeing the message below, I and no one else saw this message, and the menu works fine.

Strict standards: Declaration of Walker_Nav_Primary::start_lvl()
should be compatible with Walker_Nav_Menu::start_lvl(&$output,$depth =
0, $args = Array) in …/inc/walker.php on line 0

So he made a couple of changes the first was to address this error by putting in $args =array() in the start_lvl function which as missing, but then he writes that $args is not an object its a array so you can’t do $args->something, you have to do $args[‘something’], which gives the code;

class Walker_Nav_Primary extends Walker_Nav_menu {

    function start_lvl( &$output, $depth = 0, $args = array() ) { //ul
        $indent = str_repeat("t",$depth);
        $submenu = ($depth > 0) ? ' sub-menu' : '';
        $output .= "n$indent<ul class="dropdown-menu$submenu depth_$depth">n";
    }

    function start_el( &$output, $item, $depth = 0, $args = array(), $id = 0 ){ //li a span
        $indent = ( $depth ) ? str_repeat("t",$depth) : '';
        $li_attributes = '';
        $class_names = $value = '';
        $classes = empty( $item->classes ) ? array() : (array) $item->classes;

        $classes[] = ($args['walker']->has_children) ? 'dropdown' : '';

        $classes[] = ($item->current || $item->current_item_ancestor) ? 'active' : '';
        $classes[] = 'menu-item-' . $item->ID;
        if( $depth && $args['walker']->has_children ){
            $classes[] = 'dropdown-submenu';
        }
        $class_names =  join(' ', apply_filters('nav_menu_css_class', array_filter( $classes ), $item, $args ) );
        $class_names = ' class="' . esc_attr($class_names) . '"';
        $id = apply_filters('nav_menu_item_id', 'menu-item-'.$item->ID, $item, $args);
        $id = strlen( $id ) ? ' id="' . esc_attr( $id ) . '"' : '';
        $output .= $indent . '<li' . $id . $value . $class_names . $li_attributes . '>';
        $attributes = ! empty( $item->attr_title ) ? ' title="' . esc_attr($item->attr_title) . '"' : '';
        $attributes .= ! empty( $item->target ) ? ' target="' . esc_attr($item->target) . '"' : '';
        $attributes .= ! empty( $item->xfn ) ? ' rel="' . esc_attr($item->xfn) . '"' : '';
        $attributes .= ! empty( $item->url ) ? ' href="' . esc_attr($item->url) . '"' : '';
        $attributes .= ( $args['walker']->has_children ) ? ' class="dropdown-toggle" data-toggle="dropdown"' : '';
        $item_output = $args['before'];
        $item_output .= '<a' . $attributes . '>';
        $item_output .= $args['link_before'] . apply_filters( 'the_title', $item->title, $item->ID ) . $args['link_after'];
        $item_output .= ( $depth == 0 && $args['walker']->has_children ) ? ' <b class="caret"></b></a>' : '</a>';
        $item_output .= $args['after'];
        $output .= apply_filters ( 'walker_nav_menu_start_el', $item_output, $item, $depth, $args );
    }
}

However, when I run the code I get the following error

Fatal error: Cannot use object of type stdClass as array in

referring to lines where

$classes[] = ($args->walker->has_children) ? 'dropdown' : '';

has been changed to

$classes[] = ($args['walker']->has_children) ? 'dropdown' : '';

We are both on the same PHP and WordPress so I don’t understand why it is working for him and not me, and which is the correct method.

Can anyone shed any light?