From: Sean O'Halpin <sean.ohalpin@...>
Date: 2011-07-22T07:41:37+09:00
Subject: Re: attr_accessor for hash keys

On Thu, Jul 21, 2011 at 10:17 PM, Chad Perrin <code@apotheon.net> wrote:
> Is there a way to use attr_accessor, or something like it (without
> writing it from scratch), for hash keys?  For instance:
>
>    class Foo
>      attr_accessor :bar[:one], :bar[:two]
>      def initialize(bar)
>        @bar = bar
>      end
>    end
>
> Obviously, :bar[:one] and :bar[:two] won't work, because symbols don't
> have [] methods, but that should illustrate the general gist of what I'm
> asking (I hope).  I'd just like to avoid the clutter of writing a bunch
> of basic accessors myself, the long way, in a class definition where I'd
> like to keep all the data in a hash but have direct accessor method ways
> to work with specific key=>value pairs.
>
> --
> Chad Perrin [ original content licensed OWL: http://owl.apotheon.org ]
>

This is reasonably close to what you described:

module HashAccessor
  def hash_accessor(hash_name, *key_names)
    key_names.each do |key_name|
      define_method key_name do
        instance_variable_get("@#{hash_name}")[key_name]
      end
      define_method "#{key_name}=" do |value|
        instance_variable_get("@#{hash_name}")[key_name] = value
      end
    end
  end
end

class Foo
  extend HashAccessor
  hash_accessor :bar, :one, :two
  def initialize(bar)
    @bar = bar
  end
end

foo = Foo.new(:one => 1, :two => 2) # => #<Foo:0x9c28310
@bar={:one=>1, :two=>2}>
foo.one                             # => 1
foo.one = 42
foo                                 # => #<Foo:0x9c28310
@bar={:one=>42, :two=>2}>

Regards,
Sean