From: "Ara.T.Howard" <ahoward@...>
Date: 2004-04-24T00:44:13+09:00
Subject: Re: Problem assigning an Array object to an Array-subclass object

On Fri, 23 Apr 2004, Richard Lionheart wrote:

> [ I apologize if this is a second post.  My earlier one seems to have gotten
> lost in the ethernet :-) ]
> 
> notes =<<NOTES
>     I didn't like to_s' output for an Array of strings.
>     Array#to_s simply concatenated them
>     or inserted a comma separator.
>     So I wrote my own.
>     But as the last line indicates,  I failed.
> 
>     Apparently, array assignment to myA1
>     changed the reference from a MyArrayType object
>     to an Array object.
> 
>     Two questions:
>     1.  How can I set myA1 to an array value
>         and preserve it's type?
>     2.  Isn't there a "Ruby way" to set the separator
>     (I thought there was some special symbol a la Perl
>     but I couldn't find any in Thomas' or Fulton's
>     books.)
> NOTES
> 
> class MyArrayType < Array
>     def to_s
>         print "Starting MyArrayType#to_s"
>         s = ""
>         s.each { |x| s += "; " if s.length>0; s += x.to_s }
>         s
>     end
> end
> 
> myA1 = MyArrayType.new
> myA1 = %w[x1, y1]
> puts myA1.to_s  # x1,y1 .... expected x1; x2 .... MyArrayType#to_s not
> invoked


try this:

  class MyArrayType < Array
    def to_s
      join ';' 
    end
  end

  myA1 = MyArrayType['x1', 'y1']
  puts myA1.to_s                      # => x1;y1
  puts myA1                           # => x1\ny1


your statement:

>     Apparently, array assignment to myA1
>     changed the reference from a MyArrayType object
>     to an Array object.

was correct

what you did i just like

  myA1 = MyArrayType.new
  myA1 = 'fubar' 

so, of course, your method was not called


something else to be aware of:

  - Object#puts behaves different if passed an Array, or sub-class of Array,
    see above 

in general it can be tricky to inherit from the built-ins.
-a
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