From: Sam Roberts <sroberts@...>
Date: 2005-03-14T06:49:34+09:00
Subject: Re: how do I convince Hash that two keys are the same?

Quoting ruby-ml@magical-cat.org, on Mon, Mar 14, 2005 at 06:08:35AM +0900:
> >I think Str#downcase should return the same thing as String#downcase =>
> >a String, and not a Str, so I don't see why there is a recursive call,
> >here.
> 
> When you derive, you establish an is_a relationship. Str is_a String.
> All methods are also derived so you're actually calling Str#downcase,
> although the code being executed was defined in String.

I don't think thats the answer, its not how things normally work.

String#to_s doesn't work that way, for example, despite the docs saying
it does, it returns an object of class String, even if the receiver
isn't of class String.

It looks like String.upcase is creating a new instance of its derived
class, but somehow bypassing the derived classes initialize, see example
below.


I don't understand how it does this. I thought it might be calling
self.class.new, but it doesn't.

For example, how would I do this so it has the same behaviour as
#downcase, returning an object of the derived class:

  
  class String
    def brackets
      self.class.new("(" + self + ")")
    end
  end

The above doesn't work, so how would I do it? Hm, maybe self.copy.tr(..)
is what its doing...

I guess I should read the String src code.

Cheers,
Sam


Run the following through irb.


class String
  def brackets
    self.class.new("(" + self + ")")
  end
end
    
class Str < String
  def initialize(s)
    puts '!Str'
    super(s)
  end
end


class Now < String
  def initialize
    puts '!Now'
    super(Time.now.to_s)
  end
end

class Now2 < String
  def initialize(a,b)
    puts "!Now2 #{a} #{b}"
    super(Time.now.to_s)
  end
end

Str.new('aa').upcase
Str.new('aa').upcase.class
Now.new.upcase
Now.new.upcase.class
Now2.new(1,2).upcase
Now2.new(1,2).upcase.class

Str.new('aa').brackets
Now.new.brackets
Now2.new(1,2).brackets


Str.new('aa').to_s.class
Now.new.to_s.class
Now2.new(1,2).to_s.class