From: "Mauricio Fernández" <batsman.geo@...>
Date: 2003-09-13T21:11:46+09:00
Subject: Re: Duck Typing

On Sat, Sep 13, 2003 at 07:53:18PM +0900, Meino Christian Cramer wrote:
>   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 you see is Fixnum#[]

-------------------------------------------------------------- Fixnum#[]
     fix[ n ] -> 0, 1
------------------------------------------------------------------------
     Bit Reference---Returns the nth bit in the binary representation of
     fix, where fix[0] is the least significant bit.
        a = 0b11001100101010
        30.downto(0) do |n| print a[n] end
     produces:
        0000000000000000011001100101010

>   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]]

I guess this is only your notation and not the code you're feeding to ruby :)
 
>   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.

That's because String has an instance method named [], too.
You'd have to use is_a? Array, but I'd rather change the code so that
in the first pattern you have an array of length 1.

ie

 bla["0xff"] = [["bla", "file.rb"]]
 bla["0x01"] = [["foo", "file2.rb], ["bar", "file3.rb"]]

This way the same code can work for both cases.

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