From: why the lucky stiff <ruby-talk@...>
Date: 2004-11-27T01:36:46+09:00
Subject: Re: YAML question (hi _why!)

Hal Fulton wrote:
> This property_map isn't clear to me yet. Why not class-level data instead
> of instance?

You could certainly use a class method.

In Hobix, I like to encourage the user to override my classes and to 
create singletons to exhibit custom behavior.  Instance methods are 
simpler in this regard.

> I hadn't thought about the issue of required vs. optional. I would have
> just said: If it doesn't have a default, and it's not there, default it
> to nil.

Having required fields is nice when I am supplying the user with a blank 
object to fill in.

>> As you can see, the mixin also defines 'initialize', since you'll 
>> probably want to apply the defaults even if the object is created 
>> programmatically.
> 
> This confuses me greatly. What if a class already has an #initialize (as
> most do?).

I'm providing this default #initialize as an example of using 
#apply_defaults in the constructor.  It's okay if it's not used.

>> You'll also need to hook yourself a YAML type for each class.  In the 
>> case of the Hobix::Entry class, I'm hooking !hobix.com,2004/entry.
> 
> Argh. If I had to do this stuff every time, I'd almost rather keep using
> the hack I'm using.

If it's any reassurance, this will be simpler in Syck 0.50.  You'll 
still have to set up the property_map and use the mixin to get this 
auto-defaults behavior.  But assigning types will be as simple as:

   class Hobix::Entry
     tag_as "tag:hobix.com,2004:entry"
   end

For now, though, you'll need to do this for each class with a type:

   class Hobix::Entry
     def to_yaml_type
         "!hobix.com,2004/entry"
     end
   end

   YAML::add_domain_type( 'hobix.com,2004', 'entry' ) do |type, val|
     YAML::object_maker( Hobix::Entry, val ).apply_defaults
   end

_why