From: Gary Wright <gwtmp01@...>
Date: 2007-03-04T09:40:12+09:00
Subject: Re: Duck Typing Hash-Like Objects


On Mar 3, 2007, at 1:02 PM, Ed Howland wrote:
> This may be OT, (or merely off-base,) but somewhere else on this list
> I read about using mutators (not sure if that is the formal name or
> not) on #new. This keeps the complexity out of initialize having to
> parse each argument for its type.
>
> E.g.
>
>   my_obj = MyClass.new    # no arg ctor
>   my_obj = MyClass.new('John', 'Smith') # canon - takes strings
>   my_obj = MyClass.new.from_hash {:last_name =>  
> 'Smith', :first_name => 'John'}
>   my_obj = MyClass.new.from_arr ['John', 'Smith']

This certainly simplifies MyClass#initialize but Ruby is flexible enough
that you can create your own methods to allocate and initialize  
without going
through MyClass#initialize:

class MyClass
   class <<self
     def new_from_hash(h)
       o = allocate
       o.send(:initialize_from_hash, h)
       o
     end
   end
   attr_accessor :pairs
   def initialize_from_hash(h)
     @pairs = h.to_a
   end
   private :initialize_from_hash
end

mc = MyClass.new_from_hash({1,2,3,4})
puts mc.pairs        # [[1,2],[3,4]]


Gary Wright