Unobtrusively get the IDs of ALL posts in a WordPress query, not just the posts on the current page

gistfile1.txt

/**
 * Unobtrusively gets the IDs of all posts in the current query, not just the posts shown on the current page.
 * 
 * @author Brent Shepherd <[email protected]>
 * @since 1.0
 */
function eg_get_all_posts_in_query() {
	global $wp_query;

	// Turn paging off & specify that we only want post IDs
	$wp_query->set( 'nopaging', true );
	$wp_query->set( 'fields', 'ids' );

	$post_ids = $wp_query->get_posts();

	// Reset the query
	$wp_query->set( 'nopaging', false );
	$wp_query->set( 'fields', '' );
	$wp_query->get_posts();

	return $post_ids;
}