From: RichardOnRails <RichardDummyMailbox58407@...>
Date: 2008-05-05T12:40:06+09:00
Subject: Re: Matrix-element extractor -- How to define it

On May 4, 5:44 pm, Daniel Finnie <d...@danfinnie.com> wrote:
> Hi again,
>
> I'm glad super worked out for you.  That's the "right way" to do it
> for inheritance.
>
> I have a feeling I may have misguided you with the "alias old_[] []"
> line.  It should probably be something like "alias old_brackets []" as
> I doubt that old_[] is a valid method name (I just checked and it
> isn't, to be sure).
>
> Dan
>
> On Sun, May 4, 2008 at 4:40 PM, RichardOnRails
>
> <RichardDummyMailbox58...@uscomputergurus.com> wrote:
> > On May 3, 9:06 pm, Daniel Finnie <d...@danfinnie.com> wrote:
> >  > Hi,
>
> >  > You do this:
> >  > class Array
> >  >   alias old_[] []
> >  >   def [] *args
> >  >     if *args.length == 2 && args[0].is_a? Integer && args[1].is_a? Integer
> >  >       get(*args)
> >  >     else
> >  >       old_[](*args)
> >  >   end
> >  > end
>
> >  > Of course, this would remove some of the functionality of an Array for
> >  > every Array, not just matricies.  Consider making a subclass of Array
> >  > like this:
> >  > class Matrix < Array
> >  >   ...
> >  > end
>
> >  > Now you can modify Matrix at will without affecting Array.
>
> >  > If you are creating a Matrix for purely pragmatic reasons (i.e., not
> >  > as an excercise) then there is an excellent Matrix class in the Ruby
> >  > standard library:http://ruby-doc.org/stdlib/
>
> >  > Dan
>
> >  > On Sat, May 3, 2008 at 4:05 PM, RichardOnRails
>
> > > <RichardDummyMailbox58...@uscomputergurus.com> wrote:
> >  > > Hi,
>
> >  > >  I defined and populated a 9x9 matrix (Array of Arrays) of strings, m
>
> >  > >  I defined an element-extractor:
>
> >  > >  class Array
> >  > >         def get(i,j)
> >  > >                 line =self[i-1]
> >  > >                 char = line[j-1]
> >  > >         end
> >  > >  end
>
> >  > >  To get the first element of the second row, I used the following,
> >  > >  which worked fine:
>
> >  > >  m.get(2,1)
>
> >  > >  I'd like to write merely m(2,1).  How can I do that simply?
>
> >  > >  Thanks in Advance,
> >  > >  Richard
>
> >  Hi Daniel,
>
> >  Thanks for the "kick start" and the Matrix class.  I got the latter
> >  working,  but I'm going to "roll my own" because I want a Sudoku
> >  solver that works the way I do manually.  I know there's a free solver
> >  written in VisualProlog, but like Frank Sinatra, "I'll do it my
> >  way" :-)
>
> >  >     alias old_[] []
>
> >  I'm running ruby 1.8.6 (2007-09-24 patchlevel 111) [i386-mswin32].  It
> >  barfed on "old_", so I substituted:
> >     else
> >       super(*args)
> >  which worked fine.
>
> >  Best wishes,
> >  Richard

Hi Daniel,

Thanks for your additional response.

> misguided

No problem!  I misguide myself all the time :-)  Any, it's history.

I've got two questions about my current version of your code,  which
works fine BTW.

1.  Where is the get method come from.  I looked in Ruby RDoc and (i)
see no get method for Array, nor (ii) any related get method on the
Methods section of the RDoc.  I'd really like a pointer to it's
documentation.  It certainly is useful in this context.

2.  As I mentioned,  I switched from "old_[](*args)" in the else
clause to "super *args". which works fine for the most part.  I works
fine, too, except I want to substitute "raise 'invalid data'" or
something more descriptive.  Unfortunately,  when I do that I get a
syntax error.

If you have the time,  I'd love to get your take on these issues.
Code and output is below for your convenience.

Best wishes,
Richard

class Matrix < Array
  def [] *args
    if (args.length == 2) && args[0].is_a?(Integer) && args[1].is_a?
(Integer)
      get(*args)
    else
      super *args
		end
  end
end

m = Matrix[ [10,20,30], [40,50,60], [70,80,90] ];
puts m [0] [1]		#  20
puts m [2] [0]		#  70
puts m[1]		#  40
			#  50
			#  60

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