Group intersection question

gistfile1.yml

# This works.
tasks:
  - debug: var=hostvars[item]
    with_items: groups['groupA']

# How can I do something like:

tasks:
  - debug: var=hostvars[item]
    with_items: groups['groupA'].intersect(groups['groupB'])

# the equivalent of below
hosts: groupA:&groupB

# except inside a task.