From: "Mauricio Fernández" <batsman.geo@...>
Date: 2003-06-09T02:18:51+09:00
Subject: Re: run-time type evaluation and programming style

On Mon, Jun 09, 2003 at 12:55:44AM +0900, walter@mwsewall.com wrote:
> week I wrote a simple Object persistence manager that would let me do 
> simple crud to a db (apparently this is quite popular lately).  One 
> of the features it does have is that I encode the expected type of 
> the data going to and from the database.  I do this through the use 
> of converter objects.  I find that I need to use .class method to 
> determine the type of object that I am dealing with, in a case 
> statement, and then do what I need to based on that.  Most any time 
> that I need to use RTTI in Java it is almost certainly a violation of 
> the Open/Closed principle (OCP) for that method.  But having said 
> that by using method overloading in essence I am doing  the same 
> thing, I am using RTTI to overload the method, but the Java language 
> is doing it implicitly, in Ruby I need to do this via direct 
> evaluation inside of a method.
> 
> I guess what I am asking is this considered generally acceptable in 
> Ruby, in Java it would not normally be.  I am missing a better way to 
> accomplish this.

This does probably not apply to your situation, but when I see
  case bla.class
  when Foo
    do_foo
  when Bar
    do_bar
  end

I always think of doing

class Foo 
  def do(context)
    ...
  end
end

class Bar
  def do(context)
    ...
  end
end

and later

 some_context = ...
 bla.do(some_context)   # let method dispatch decide what is appropriate

This way you don't have to update 10 case statements if you add a new
class, which I see as a good example of DRY. 

The following is somewhat tangential but interesting nonetheless:
http://www.rubygarden.org/ruby?CoerceExplanation

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