[chef] Re: Re: Re: Re: Re: Re: Re: Re: deep merge - !merge users

[Matthew Kent < >]

<snip>
On Fri, Dec 9, 2011 at 9:24 AM, Daniel DeLeo 
<
 >
 wrote:
<snip>
> It's easy to imagine a case where you'd want to *subtract* values, say, 
> removing port 80 from an Array specifying which ports httpd should listen 
> on. And in fact, Chef's deep merging has some support for this, by 
> inserting special "!merge:" values in your attributes.
>
> While one can imagine uses for this "subtractive merging," in practice no 
> one uses it, and simply by its existence, the computational and memory 
> requirements of the merging algorithm are increased substantially. This is 
> a big deal when you're, say, iterating over a large set of nodes returned 
> from a search result--a much more common use case.
>
> The alternative existing mechanisms you could use to subtract values from 
> attributes (modify the cookbook, use a "proxy" cookbook to forcibly set the 
> attributes correctly) aren't very pretty either, but I think they'd at 
> least lead you to a more declarative result, and be easier for everyone on 
> your team to follow.

Thanks for this summary and positioning statement - sounds like
there's not much interesting in merging CHEF-2737 so I've closed it
for now.

I'll file another ticket for cleaning up the existing 0.10 role
!merge: behaviour and I'll update the deep merge doc for
clarification.

I'm guessing in 0.11 you'd like the !merge subtraction removed
entirely? Only so I can mention this in the code/docs as well.
Certainly would reduce the code gymnastics in the deep merge mixin and
specs...
-- 
Matthew Kent | http://magoazul.com