-- Icanhaz mai var, Ansible? -- Not after 2.8 of me!

inc1.yml

- name: Return task result in a variable named in 'ret'
  debug: msg="My first argument is {{ arg1 | default("undefined!") }}"
  register: "{{ ret }}"

main.yaml

- hosts: localhost
  gather_facts: no
  vars:
    var_a: "dynamic include AAA"
    var_b: "dynamic include_tasks BBB"
    var_c: "static import_tasks CCC"
  tasks:
    - name: Check ret0 before task include.
      debug: msg="ret0 is {{ ret0 | default("undefined!") }}"

    - name: You wouldn't see this 'name' in output (
      include: inc1.yml
      vars:
        arg1: "{{ var_a }}"
        ret: ret0
    - name: Check returned var
      debug: msg="ret0 is {{ ret0 | default("undefined!") }}"

    - name: Run inc1.yml with 'include_tasks'.
      include_tasks: inc1.yml
      vars:
        arg1: "{{ var_b }}"
        ret: ret0
    - name: Check returned var
      debug: msg="ret0 is {{ ret0 | default("undefined!") }}"

    - name: Neither would you see this 'name'!
      import_tasks: inc1.yml
      vars:
        arg1: "{{ var_c }}"
        ret: ret0
    - name: Check returned var
      debug: msg="ret0 is {{ ret0 | default("undefined!") }}"

This is my version of a wonderful answer given 2017-05-23 18:43:28Z to a question "How can Ansible 'register' in a variable the result of included playbook?"

Works OK in Ansible 2.7.6 but not in 2.8.0dev0.