From: Robert Klemme <shortcutter@...>
Date: 2008-07-27T23:59:46+09:00
Subject: Re: "nested" methods

On 27.07.2008 16:02, Stefan Buhr wrote:
> I want to do this:
> 
> @myclass.items[5] = an_item
> 
> But the items object of @myclass should have an custom setter. I have
> tried this:
> class Myclass
>     def items
>         def []= value
>             -code-
>         end
>     end
> end
> 
> but this does not work.

Your nested method is defined for Myclass.  Basically something like 
nested methods does not exist in Ruby.  The only difference is the point 
in time when the nested method will be defined (after the other method 
has been executed):

$ irb
irb(main):001:0> class M
irb(main):002:1> def x
irb(main):003:2> def y; 9; end
irb(main):004:2> end
irb(main):005:1> end
=> nil
irb(main):006:0> m=M.new
=> #<M:0x7ff8a1e0>
irb(main):007:0> m.y
NoMethodError: undefined method `y' for #<M:0x7ff8a1e0>
         from (irb):7
irb(main):008:0> m.x
=> nil
irb(main):009:0> m.y
=> 9
irb(main):010:0> m=M.new
=> #<M:0x7ff7888c>
irb(main):011:0> m.y
=> 9
irb(main):012:0>


> How can i do that?

class Myclass
   def items
     @items ||= []
   end
end

Now you have a member of type Array in Myclass and can use its method []=.

You can as well do this

class Myclass
   class Items
     def []= idx, val
       # whatever
     end
   end

   def items
     @items ||= Items.new
   end
end

Kind regards

	robert