[openstack-dev] [Solum] Some initial code copying for db/migration

Jay Pipes jaypipes at gmail.com
Tue Nov 19 00:09:12 UTC 2013

On 11/18/2013 04:58 PM, Christopher Armstrong wrote:
> On Mon, Nov 18, 2013 at 3:00 PM, Dan Smith <dms at danplanet.com
> <mailto:dms at danplanet.com>> wrote:
>     Sorry for the delay in responding to this...
>      >   * Moved the _obj_classes registry magic out of ObjectMetaClass
>     and into
>      >     its own method for easier use.  Since this is a subclass
>     based implementation,
>      >     having a separate method feels more appropriate for a
>     factory/registry
>      >     pattern.
>     This is actually how I had it in my initial design because I like
>     explicit registration. We went off on this MetaClass tangent, which buys
>     us certain things, but which also makes certain things quite difficult.
>     Pros for metaclass approach:
>       - Avoids having to decorate things (meh)
>       - Automatic to the point of not being able to create an object type
>         without registering it even if you wanted to
>     Cons for metaclass approach:
>       - Maybe a bit too magical
>       - Can make testing hard (see where we save/restore the registry
>         between each test)
>       - I think it might make subclass implementations harder
>       - Definitely more complicated to understand
>     Chris much preferred the metaclass approach, so I'm including him here.
>     He had some reasoning that won out in the original discussion, although
>     I don't really remember what that was.
> It's almost always possible to go without metaclasses without losing
> much relevant brevity, and improving clarity. I strongly recommend
> against their use.



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