[openstack-dev] [Heat] New function: first_nonnull

Fox, Kevin M Kevin.Fox at pnnl.gov
Thu Nov 6 15:53:43 UTC 2014

Except it penalizes us bad spellers. ;)


From: Clint Byrum
Sent: Wednesday, November 05, 2014 11:26:43 PM
To: openstack-dev
Subject: Re: [openstack-dev] [Heat] New function: first_nonnull

Excerpts from Lee, Alexis's message of 2014-11-05 15:46:43 +0100:
> I'm considering adding a function which takes a list and returns the first
> non-null, non-empty value in that list.
> So you could do EG:
>     some_thing:
>         config:
>             ControlVIP:
>                 first_nonnull:
>                 - {get_param: ControlVIP}
>                 - {get_attr: [ControlVirtualIP, fixed_ips, 0, ip_address]}]}
> I'm open to other names, EG "some", "or", "fallback_list" etc.
> Steve Hardy suggested building this into get_attr or Fn::Select. My feeling
> is that those each do one job well right now, I'm happy to take a steer
> though.
> What do you think please?

Yes this is super useful for writing responsive, reusable templates.

I'd like to suggest that this be called 'coalesce' as that is what SQL
calls it.

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