From: Jim Freeze <jim@...>
Date: 2002-12-14T21:45:54+09:00
Subject: Re: Inheritance Question

On Saturday, 14 December 2002 at 19:45:03 +0900, ts wrote:
> >>>>> "a" == ahoward  <ahoward@fsl.noaa.gov> writes:
> 
> a> p ((mm + Matrix[[12]]).type) 	# >> MyMatrix
> a> p ((Matrix[[12]] + mm).type) 	# >> Matrix
> a> p ((mm + mm).type          ) 	# >> MyMatrix
> 
>  Now you have a big problem, because this not what ruby do
> 
> pigeon% cat b.rb
> #!/usr/bin/ruby
> class A < Array; end
> a = A.new
> p ((a+[]).class)
> p (([]+a).class)
> p ((a+a).class)
> pigeon% 
> 
> pigeon% b.rb
> Array
> Array
> Array
> pigeon% 

Don't you mean that this is how Array was implemented, not what
ruby does. Maybe Array is not doing the right thing by not
returning self (I'm sure someone will correct me here if I am wrong). 
The language doesn't force one to always return the base class.

class A
  def +(o)
    self
  end
end

class B < A
  def +(o)
    self
  end
end

a=A.new
b=B.new

p ((a+a).class)  #=> A
p ((b+b).class)  #=> B
p ((a+b).class)  #=> A
p ((b+a).class)  #=> B


-- 
Jim Freeze