Theming a table '#type' vs '#theme'

Question

I am dynamically rendering a table in a Drupal 8 module. While creating my renderable array I noticed that I can define my table as a '#theme' => 'table' or as '#type' => 'table'.

$variables['test_table'] = [
    '#theme' => 'table',
    '#header' => $header,
    '#rows' => $rows,
    '#attributes' => array('class'=>array('my-table')),
    '#header_columns' => 4,
];

vs:

$variables['test_table'] = [
    '#type' => 'table',
    '#header' => $header,
    '#rows' => $rows,
    '#attributes' => array('class'=>array('my-table')),
    '#header_columns' => 4,
];

Both of these options seem to output the same thing.

My question is this: Why can I use either '#theme' => 'table' or '#type' => 'table' when defining a table renderable array and is there any difference between how Drupal will render these differently.

Answer 1

I believe ultimately both will do the same thing. But when you use 'type' you are referring to what drupal element to use (see https://api.drupal.org/api/drupal/elements) and when you use '#theme' you're directly telling it what twig template to use.

Answer 2

As Matt already said, the advantage of using #type is that you can have standard render array children instead of using #rows, which you shouldn't use with #type but works because it's basically just a wrapper that eventually uses `'#theme' => 'table' internally.

That allows to put form elements inside a table. In 7.x, this was always a pain that required custom theme functions to reshuffle a form structure back into something that the table template understands.