ansible - example of setting a complex var with set_fact

output

PLAY [foo] ********************************************************************

GATHERING FACTS ***************************************************************
ok: [localhost]

TASK: [set_fact ] *************************************************************
ok: [localhost]

TASK: [debug ] ****************************************************************
ok: [localhost] => {
    "var": {
        "complex_arg": [
            {
                "address": "mars",
                "name": "bob"
            },
            {
                "name": "mary"
            }
        ]
    }
}

play.yml

---
- hosts: foo
  tasks:
    - set_fact:
        complex_arg:
          - name: bob
            address: mars
          - name: mary

    - debug:
        var: complex_arg

play2.yml

---
- hosts: foo
  tasks:
    # or with a json value
    - set_fact:
        complex_arg: '[{"name":"bob", "address":"mars"},{"name":"mary"}]'

    - debug:
        var: complex_arg

play3.yml

---
- hosts: foo
  vars:
    complex_arg: '[{"name":"bob", "address":"mars"},{"name":"mary"}]'
  tasks:
    - set_fact: complex_arg
    - debug:
        var: complex_arg

all plays give the same output.