From: "trans.  (T. Onoma)" <transami@...>
Date: 2005-01-14T05:43:25+09:00
Subject: Re: Duck Typing as Pattern Matching

On Thursday 13 January 2005 01:34 pm, E S wrote:
| > L辰hett辰j辰: "trans.  (T. Onoma)" <transami@runbox.com>
| > Aihe: Re: Duck Typing as Pattern Matching
| >
| > I haven't read the entire thread so forgive me if I'm rehashing....
| >
| > On Thursday 13 January 2005 09:51 am, itsme213 wrote:
| > | "ts" <decoux@moulon.inra.fr> wrote in message
| > |
| > | > p txn.respond_to?(:create_modify)
| > | > p txn.create_modify
| > |
| > | Oh oh, even more Ruby experts join the chorus ? :-)
| > |
| > | My claim is this: If you redefine #method_missing so your object
| > | handles x.foo as the caller would expect, then you _should_ define
| > | x.respond_to?(:foo) to return true. I do not claim that Ruby should
| > | prohibit code that does not do this.
| >
| > I wonder if method missing would be better if these two "tiers" were
| > built in to it. This would require dual "blocks" so I'm not sure how to
| > notate it but:
| >
| >   def method_missing(meth, *args)
| >   upon meth == :create_modify
| >     # do whatever
| >   upon ...
| >     # ...
| >   end
| >
| > Then #respond_to? can utilize the "upon" block to determine responses
| > correctly.
|
| Are you thinking something different than
|
| def method_missing(meth, *args)
|   case meth
|     when :create_modify
|       # ...
|   end
| end
|

Yes. A bit different on two accounts. 1) The "upon" clause is just a regular 
boolean returning block, like #if, not divided and limited to matching like 
#case is. And 2) it would be instrumental to how #method_missing works, thus 
in some manner queryable, so that #respond_to? and potentially other methods 
could make use of it. That's the idea any way. There may very well be a 
better way to achieve the same goal.

T.