From: Brian Candler <b.candler@...>
Date: 2011-02-04T17:56:01+09:00
Subject: Re: Setter method for Hash value

Rolf Pedersen wrote in post #979464:
> Hi Brian (and others who have contributed with suggestions along the
> same
> line)
>
> It's not the class MyClass that I'd like to behave like a Hash.
> I'm trying to make getter and setter methods for a virtual hash property
> called props.

Then the 'props' object which you return needs methods [] and []= 
defined, which do whatever you want them to do.

I see you are using these methods on the class itself (not instances of 
the class):

    SomeClass::set_prop(key, value)

In that case, you can define them as class methods:

    class SomeClass
      def self.[](key)
        get_prop(key)
      end
      def self.[]=(key,value)
        set_prop(key,value)
      end
    end

And then simply return the class itself:

    class MyClass
       def props
         SomeClass
       end
     end

If you were using *instances* of SomeClass, then personally I would just 
define methods [] and []= as instance methods. Depending on how 
Hash-like you want this object to be, you may want to define some other 
methods too.

If there is some particular reason why you can't do that, then you would 
have to return a proxy object, whose [] and []= methods are relayed to 
get_prop and set_prop on the underlying SomeClass object.

If you still want props to return an actual Hash, then it will have to 
be a Hash which has been modified so that []= performs the operation on 
the underlying object.

You can use delegate.rb, or you can explicitly delegate those methods 
which you want to. Here is some code from CouchTiny which wraps a Hash:

module CouchTiny
  # A class which delegates a small subset of methods to a Hash (to keep
  # the space as clear as possible for accessor names)
  class DelegateDoc
    attr_accessor :doc

    def initialize(doc = {})
      @doc = doc.to_hash
    end

    def to_hash
      @doc
    end

    def ==(other)
      @doc == other # .to_hash is done by Hash#==
    end

    def to_json(*args)
      @doc.to_json(*args)
    end

    alias :orig_respond_to? :respond_to?
    def respond_to?(*m)
      orig_respond_to?(*m) || @doc.respond_to?(*m)
    end

    def [](k)
      @doc[k.to_s]
    end

    def []=(k,v)
      @doc[k.to_s] = v
    end

    def key?(k)
      @doc.key?(k)
    end

    def has_key?(k)
      @doc.has_key?(k)
    end

    def delete(k)
      @doc.delete(k)
    end

    def merge!(h)
      @doc.merge!(h)
    end

    def update(h)
      @doc.update(h)
    end

    def dup
      self.class.new(@doc.dup)
    end

    #def method_missing(m, *args, &block)
    #  @doc.__send__(m, *args, &block)
    #end
  end
end


Regards,

Brian.

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