Smarty:如何引用关联数组索引

$my_array = array(
    'apple' => 'fruit',
    'carrot' => 'vegetable',
    'chicken' => 'meat'
);

$smarty->assign('my_array', $my_array);

{foreach from=$my_array key=key item=value}
    {$key}: {$value}<br>
{/foreach}

apple: fruit
carrot: vegetable
chicken: meat