Pass a PHP array to Twig?

I want to be able to access an array in my Twig template that is built in PHP but it always appears blank, am I missing something?

mytheme.theme

function mytheme_preprocess_page(array &$variables) {
  $variables['myvar'] = 'foo';
}

page.html.twig

{{ myvar }}

works as expected but if I pass an array this doesn't work:

$variables['myvar'] = ['foo', 'bar'];

just outputs nothing

There are two possible answers depending on what you are trying to achieve. You can loop over arrays in Twig like in any programming language, see the other answer.

Specific to Drupal's template engine is that if you want Twig to render an array recursively it has to be a renderable array. This means that each element which has no children has to be a render element (#markup, #plain_text, #type or #theme):

$variables['myvar'] = [
  0 => ['#plain_text' => 'foo'],
  1 => ['#plain_text' => 'bar'],
];

Then

{{ myvar }}

renders the entire array.

See https://www.drupal.org/docs/drupal-apis/render-api/render-arrays.

To print all the items contained in that array without assuming how many items it contains, you can use the following code.

{% for key, var in myvar %}
  {{ myvar[key] }}
{% endfor %}  

Otherwise, you can simply use the following code.

{{ myvar[0] }} {{ myvar[1] }}