Want to reacht this vars:
ok: [localhost] => (item=app) => {
    "app": [
        {
            "name": "bla",
            "version": 1
        }
    ],
    "item": "app"
}
ok: [localhost] => (item=app_bla) => {
    "app_bla": [
        {
            "name": "blub",
            "version": 1
        }
    ],
    "item": "app_bla"
}

They are in a vars file:
[root@websrv01 ansible]# cat version
app:
  - name: bla
    version: 1

app_bla:
  - name: blub
    version: 1

now i got this inventory file:
[root@websrv01 ansible]# cat hosts

[app]
localhost

[app_bla]
localhost


and trying to install packages on all hosts that are member of the group with this play:

  - debug: msg="going to install {{item.0.name}}-{{item}} on {{inventory_hostname}}"
    with_items: group_names

Output:

TASK [debug] *******************************************************************
[DEPRECATION WARNING]: Using bare variables is deprecated. Update your playbooks so that the environment value uses the full variable syntax ('{{group_names}}').
This feature will be
removed in a future release. Deprecation warnings can be disabled by setting deprecation_warnings=False in ansible.cfg.
fatal: [localhost]: FAILED! => {"failed": true, "msg": "the field 'args' has an invalid value, which appears to include a variable that is undefined. The error was: 'unicode object' has no attribute 'name'\n\nThe error appears to have been in '/etc/ansible/play.yml': line 8, column 5, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n    with_items: group_names\n  - debug: msg=\"going to install {{item.name}}-{{item.version}} on {{inventory_hostname}}\"\n    ^ here\nWe could be wrong, but this one looks like it might be an issue with\nmissing quotes.  Always quote template expression brackets when they\nstart a value. For instance:\n\n    with_items:\n      - {{ foo }}\n\nShould be written as:\n\n    with_items:\n      - \"{{ foo }}\"\n"}