From: Michael Neumann <neumann@...>
Date: 2001-09-21T08:49:51+09:00
Subject: [ruby-talk:21475] Re: chain methods inside and outside the class;	 how to intermingle mine and Strings' methods?

Tobias Reif wrote:
> Frykholm, Niklas wrote:
> 
> 
> > With this modification you can do this. h.upcase in String does not
> > return a String, it returns an object of the same type as h (in
> > this case a HoX). This is what makes it possible to chain calls in
> > this way.
> > 
> > Your class, HoX should be as polite, that is why delete_digits
> > should use self.class.new rather than HoX.new, it makes it possible
> > for someone to create a subclass of HoX and chain the method
> > calls.
> 
> 
> Here is the new version, thanks a lot.
> 
> But I have a new question:
> 
> --file begin--
> 
> class HoX < String
> 
>    def delete_digits
>      self.class.new self.gsub /\d/,''
>    end
> 
>    def repeat
>      self.class.new self.dup * 2
>    end
> 
>    def all
>      delete_digits.repeat
>    end
> 
> end
> 
> h = HoX.new 'a1b1c1'
> 
> # works, because h.upcase returns a HoX
> intermingled01 = h.repeat.upcase.delete_digits
> puts intermingled01 # -> ABCABC
> 
> # doesn't work, because h.reverse returns a String
> # intermingled02 = h.repeat.reverse.delete_digits
> # puts intermingled02 # -> ~ "undefined method 'delete_digits' for 
> "...":String"

Write a Delegator class that delegates all String methods to the internal-hold
String object, checks if the return value of it is a String, in which case you
create a new HoX object that holds the String internally.

class HoX 
  
  def initialize(str)
    @str = str
  end

  def to_s
    @str
  end

  def method_missing(id, *args, &b)
    ret = @str.send(id, *args, &b)
    if ret.is_a? String
      type.new(ret) 
    else
      ret
    end
  end

  def delete_digits
    type.new( @str.gsub(/\d/,'') )
  end

  def repeat
    type.new( @str.dup * 2 )
  end

  def all
    delete_digits.repeat
  end

end


--------

Regards,

  Michael

-- 
Michael Neumann
merlin.zwo InfoDesign GmbH
http://www.merlin-zwo.de