From: Meino Christian Cramer <Meino.Cramer@...>
Date: 2003-09-13T19:53:18+09:00
Subject: Re: Duck Typing

From: Hal Fulton <hal9000@hypermetrics.com>
Subject: Re: Duck Typing
Date: Sat, 13 Sep 2003 17:13:17 +0900

Hi Hal,
 
 thanks for your reply ! 

> Don't misunderstand. David is saying that this is *some* people's
> impression of what duck typing means.
> 
> Note the second part: "--when in fact it's really Ruby that's doing
> the duck typing, and you're just deciding how to react to it."
> 
> It's not a coding style or technique; it's an attribute of the
> language.

  Ok...but to use this type of duck inside of ruby...I have code
  /something/... and if something else seems (at least to me... ;) do
  the same trick...I am curious why it is better to trigger that duck
  inside of ruby. Or am I still wrong here...

  Another code snippet I did in irb gaves me headaches also. Here it
  is:

  >> a=Array.new                      // a shiny new array, full of ducks ;) 
  => []                            
  >> a=[[1,2],3]                      // fill in some extra ducks
  => [[1, 2], 3]
  >> a.respond_to?(:[])               // check whether we have an array
  => true                             // expected...
  >> a[0].respond_to?(:[])            // check wether first entry itself is
                                      // an array
  => true                             // ok, expected, too
  >> a[1].respond_to?(:[])            // now the "pure " 3...is it an array, too ?
  => true                             // OH! SURPRISE! It is an array...! (?)
  >> b=a[1]                           // lets put it in a clean variable
  => 3
  >> b.respond_to?(:[])               // now...
  => true                             // Again ... it seems to array-able

  What do I wrong here???

  Background is the following:

  I have either an hash of the following pattern

  a=Hash.new

  a=["<hexnum>", ["<id>","filename]]

  OR of that pattern:
  
  a=["<hexnum>", [["<id>","filename],["<id>","filename],....]]	

  To print both versions, I have handle the value of the hash differently.

  Currently my method tries to figure out, how to print, with the
  help of "respond_to?".

  And it fails due to the above things I did in irb.

  I am sure, that I have something understood totally wrong
  here...but...

  Kind regards,
  Meino

   
  

 
> Hal
> 
> 
>