From: Anders Borch <spam@...>
Date: 2003-06-09T03:56:55+09:00
Subject: Re: run-time type evaluation and programming style

Mauricio Fern�ndez wrote:
> 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
> 

this is probably a good idea and I should do this some more...

A.

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4dd*od3*dddn1-89danrn10-dan3+ann6*dan*2*an13dn1+dn2-dn3+5*ddan2/9+an13nap