[ruby-core:44133] Re: [ruby-trunk - Feature #4264] General type coercion protocol for Ruby

On Thu, Apr 05, 2012 at 12:28:38AM +0900, headius (Charles Nutter) wrote:
> 
> Issue #4264 has been updated by headius (Charles Nutter).
> 
> 
> Yusuke: Individual classes can (and often should) still define their own to_a, etc. There's no reason to move the current logic into a slower case/when statement.
> 
> The convert_to(cls) method would just be a standard way to allow new libraries to handle arbitrary object types without monkey-patching. For example, rather than monkey-patching a to_xml into Object or BasicObject, an XML library could just define XML.convert(obj) that contains that logic. Users would then just call obj.convert_to(XML).

So implementation would just be something like this:

  class Object
    def convert_to obj
      obj.convert self
    end
  end

It seems very nice.  Hopefully it would discourage people from monkey
patching things like `to_json` on to object.  This type of monkey
patching is a real world problem we (the Rails team) has to deal with.
Several JSON libraries would implement `to_json`, and when people had
them both activated at the same time, things would explode.

Fortunately we've worked around those issues.

I think this will help mitigate the "multi-monkey patch" problem, but as
long as people can monkey patch, those types of bugs will happen. :(

-- 
Aaron Patterson
http://tenderlovemaking.com/