From: matt@... (matt neuburg)
Date: 2006-10-17T13:45:05+09:00
Subject: Re: dynamically assigning instance variables (redux)

Phrogz <gavin@refinery.com> wrote:

> Bil Kleb wrote:
> >   Is there a way to dynamically assign instance variables?
> [...snip...]
> > Actually, I'd like the assignment and make them attr_readers too.
> 
> class Foo
>   def initialize( hash={} )
>     hash.each{ |key,value|
>       var_name = "@#{key}"
>       instance_variable_set( var_name, value )
>       singleton_class = class << self; self; end
>       singleton_class.class_eval{
>         define_method( key ){
>           instance_variable_get( var_name )
>         }
>         define_method( "#{key}=" ){ |new_value|
>           instance_variable_set( var_name, new_value )
>         }
>       }
>     }
>   end
> end

Wow, that was way cool. I think we can make it shorter (esp since he
only wants attr_readers) and faster (no point generating the singleton
class every time thru the loop):

class Foo
  def initialize( hash={} )
    singleton_class = class << self; self; end
    hash.each do |key,value|
      instance_variable_set( "@" + key, value )
      singleton_class.class_eval { attr_reader key }
    end
  end
end

f = Foo.new "name"=>'whee', "age"=>12
p f.age, f.name # => works
f.name = "no, it's a reader" # => error, as desired

But pls note that I'm just imitating; the self-returning singleton class
was totally beyond me! m.

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