ansible - example of using default() with different var states

00_play.yml

---
- hosts: localhost
  gather_facts: false
  vars:
    foo: ''
    bar: foo
    #abc
    xyz: true
  tasks:
    - debug:
        msg: "{{ foo|default(false) }}"

    - debug:
        msg: "{{ foo|default(false, true) }}"

    - debug:
        msg: "{{ bar|default(false) }}"

    - debug:
        msg: "{{ bar|default(false, true) }}"

    - debug:
        msg: "{{ abc|default(false) }}"

    - debug:
        msg: "{{ abc|default(false, true) }}"

    - debug:
        msg: "{{ xyz|default(false) }}"

    - debug:
        msg: "{{ xyz|default(false, true) }}"

01_output

PLAY [localhost] *********************************************************************************************************************************************************************

TASK [debug] *************************************************************************************************************************************************************************
ok: [localhost] => {
    "msg": ""
}

TASK [debug] *************************************************************************************************************************************************************************
ok: [localhost] => {
    "msg": false
}

TASK [debug] *************************************************************************************************************************************************************************
ok: [localhost] => {
    "msg": "foo"
}

TASK [debug] *************************************************************************************************************************************************************************
ok: [localhost] => {
    "msg": "foo"
}

TASK [debug] *************************************************************************************************************************************************************************
ok: [localhost] => {
    "msg": false
}

TASK [debug] *************************************************************************************************************************************************************************
ok: [localhost] => {
    "msg": false
}

TASK [debug] *************************************************************************************************************************************************************************
ok: [localhost] => {
    "msg": true
}

TASK [debug] *************************************************************************************************************************************************************************
ok: [localhost] => {
    "msg": true
}