Get custom post type?

So I am currently trying to get the current post type in a class. Unfortunately it seems like due to me trying to get it in the construct it is not returning the correct value. I attempted the following but it is not doing it correctly. Have been unable to find how to do it in the construct.

$post_type = get_post_type($post->ID);
if ($post_type == 'some_cpt') {
//do something
}