What hook_form_alter code do I need to change an exposed filter from a text field to a select box search?
If you would like to go for specific implementation using hook alter this would be great option.

function mymodule_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  if ($form_id == 'views_exposed_form') {
    $view = $form_state['view'];
    if ($view-&gt;name == 'my_view_machine_name' &amp;&amp; $view-&gt;current_display == 'display_name') {
      // alter your exposed form here
      $addition[$field_name] = array(
        '#attributes' =&gt; array(
          'class' =&gt; array(
            // you can define you class overhere
          ),
        ),
      ),
    }
  }
}