[chef-dev] Re: Re: Re: Re: CHEF-3762: LWRP DSL for subclassing needed?

Chronological Thread 
  • From: Jay Feldblum < >
  • To: Noah Kantrowitz < >
  • Cc: " Dev" < >
  • Subject: [chef-dev] Re: Re: Re: Re: CHEF-3762: LWRP DSL for subclassing needed?
  • Date: Mon, 28 Jan 2013 18:45:20 -0500

One option for the helpers is to move the helpers into a mixin which is included by in the lightweight base classes, and which may be included explicitly in any non-lightweight resource or provider class.

What confuses many people, from what I've seen in IRC and elsewhere, is that they're not sure how the lightweight resource and provider DSL's are a very thin wrapper around just writing yourself a resource or provider class. It's not terribly useful to re-implement Ruby inside of a Ruby-based embedded DSL just for the kicks. Better that it be explicitly clear how the lightweight DSLs are a thin wrapper around writing your own resource and provider classes, and that people learn the structural relationship between the two superficial alternatives.

- Jay

On Mon, Jan 28, 2013 at 6:15 PM, Noah Kantrowitz < " target="_blank"> > wrote:

On Jan 28, 2013, at 3:11 PM, Daniel DeLeo wrote:

> On Monday, January 28, 2013 at 3:06 PM, Noah Kantrowitz wrote:
>> On Jan 28, 2013, at 2:45 PM, Bryan McLellan wrote:
>>> http://tickets.opscode.com/browse/CHEF-3762
>>> There's been some talk about adding a DSL for subclassing LWRPs. I've heard both sentiments that it would be useful and questions if it makes something justifiably easier.
>>> Can those promoting it make a case? Can anyone else soap box about their own experience?
>> I've been pushing hard for this for a long time now. As some examples of places this would be directly useful, I've spent part of today reviewing a new Mercural resource/provider which has to subclass Chef::Resource::Scm and as such can't use the simpler LWRP syntax. Another example is any of the multitude of service resources which currently either duplicate code or use the "heavy" syntax. Beyond just subclassing built-in pieces, the application cookbook would gain a lot by allowing subclassing of individual sub-resources in places where things were mostly like a standard deployment but just need a little tweak, like (to use Django examples because that is what I'm familiar with) a requirements.txt in a non-standard place, or setting up the database connection a little differently. This would allow much more fine-grained overriding than is possible right now within the bounds of the LWRP system, and hopefully would reduce the number of times people copy-paste-fork parts of upstream cookbooks. In my bright and glorious LWRP-ified future this will only get more important over time, as I hope more cookbooks use LWRPs to provide internal modularity like this, just as you would see in any other OO API.
>> --Noah
> Once you know about subclassing and so on, is it really that onerous to use the "heavy" syntax?
>     class FooProvider < Chef::Provider::Scm
>     end
> ...doesn't seem like a ton of work.

Helpers like #attribute and #action don't work in non-LWRP files as far as I know. More to the point it confuses people seeing "heavy" resource and providers living under libraries/, so I think we should try to minimize the need for them. Additionally is there any negative to this change? It makes LWRPs more flexible without adding complexity unless you specifically request it as an author. Those that don't want to subclass things can just ignore the new functionality entirely.


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