From: Chris White <cwprogram@...>
Date: 2011-08-15T01:50:28+09:00
Subject: Re: class inheritance and class constants


On Aug 14, 2011, at 9:31 AM, Iņaki Baz Castillo wrote:

> ------------------------
> class A
>  HELLO = "Hello I'm A"
> 
>  def hello
>    puts HELLO
>  end
> end
> 
> class B < A
>  HELLO = "Hello I'm B"
> 
>  def hello2
>    puts HELLO
>  end
> end
> ------------------------
> 
> B.new.hello
> => "Hello I'm A"   (ouch...)
> 
> B.new.hello2
> => "Hello I'm B"
> 

Correct, since the method is being called in the context of A, it will search starting from A. You can verify this by printing out the Module.nesting value which is used for constant lookup searching:

-------------------------
class A
 HELLO = "Hello I'm A"

 def hello
   p Module.nesting
   puts HELLO
 end
end
-------------------------

This will output [A].

> So, if a contstant appears within a method, its value is evaluated for
> the class in which such method is defined ("hello" is defined in class
> A not in B, so it takes HELLO from class A).
> I don't like this behavior (just my opinion). Do I miss something?

This behavior can fortunately be overridden by simply overriding the hello method in the B class, meaning that it will use the constant defined in B instead:

--------------------------
class A
 HELLO = "Hello I'm A"

 def hello
   puts HELLO
 end
end

class B < A
 HELLO = "Hello I'm B"

 def hello
  puts HELLO
 end

 def hello2
   puts HELLO
 end
end

B.new.hello
--------------------------

Regards,
Chris White
http://www.twitter.com/cwgem