WordPress at a glance
filter is not described

comments_open filter-hook . WP 2.5.0

Filters whether the current post is open for comments.

Usage

add_filter( 'comments_open', 'filter_function_name_8431', 10, 2 );
function filter_function_name_8431( $open, $post_id ){
	// filter...

	return $open;
}
$open(true/false)
Whether the current post is open for comments.
$post_id(int)
The post ID.

Where the hook is called

comments_open()
wp-includes/comment-template.php 1210
return apply_filters( 'comments_open', $open, $post_id );

Where the hook is used (in WP core)

wp-includes/default-filters.php 243
add_filter( 'comments_open', '_close_comments_for_old_post', 10, 2 );