From: Lars Olsson <lasso@...>
Date: 2011-04-14T17:35:25+09:00
Subject: Re: Copying parameters to singleton class

On 14 Apr, 03:09, 7stud -- <bbxx789_0...@yahoo.com> wrote:
> 7stud -- wrote in post #992632:
>
> > Try something like this:
>
> >    def using(new_options)
> >       Class.new(self) do
> >         old_options = superclass.options
> >         common_keys = old_options.keys & new_options.keys
>
> >         common_keys.each do |key|
> >           old_options[key] = new_options[key]
> >         end
>
> >         @options = old_options
> >         @options.freeze
> >       end
> >     end
>
> Whoops.  That doesn't work:
>
> prog.rb:18:in `[]=': can't modify frozen hash (RuntimeError)
>
> Hmmm...why can you merge() but not directly assign to individual keys
> when a hash is frozen?
>
> Ok, merge() with some better variable names:
>
>    def using(new_options)
>       Class.new(self) do
>         old_options = superclass.options
>
>         @options = old_options.merge(new_options).select do |key|
>            old_options.has_key?(key)
>         end.freeze
>       end
>     end
>
> --
> Posted viahttp://www.ruby-forum.com/.

Hi!

Even though I agress that using the same name for both the local
parameter and a method with the same name might be a bad idea, my code
still works without any problem. If I redefine self using to:

(minor change to last version. I split up the calls to merge, select,
and freeze to its own rows.)

  def self.using(options)
    Class.new(self) do
      puts "Superclass options: #{superclass.options.inspect}"
      puts "Options from parameter: #{options}"
      @options = superclass.options.merge(options)
      @options.select! { |key, value| superclass.options.has_key?
(key) }
      @options.freeze
    end
  end

it clearly shows that options (by itself) refers to the local paramter
and not the class name.

/lasso