From: Sam Smoot <ssmoot@...>
Date: 2007-01-20T07:50:10+09:00
Subject: Re: Declaring instance variables dynamically


Alex Schearer wrote:
> I was curious whether there was any way to do so without employing a
> hash table

Here you go:

> class User
>   attr_accessor :name
> end
=> nil
> me = User.new
> me.name = 'Sam'
=> 'Sam'
> you = User.new
> you.name = 'Alex'
=> 'Alex'
> you.mood = :happy
=> NoMethodError...
> you.class.send(:attr_accessor, :mood)
> you.mood = :happy
=> :happy
> me.mood = :potato
=> :potato

So you can extend classes at run-time any number of ways, this is just
one of them. You can make it more magical with method_missing and a
combination of instance_variable_get and instance_variable_set too:

> module Magic
>   def method_missing(sym, *args)
>     name = sym.to_s
>     if name[-1,1] == '='
>       instance_variable_set("@#{name[0, name.size - 1]}", *args)
>     else
>       instance_variable_get("@#{name}")
>     end
>   end
> end
=> nil
> class Person
>   include Magic
> end
=> nil
> p = Person.new
> p.name = 'Alex'
=> 'Alex'
> p.mood = :peppy
=> :peppy
> puts p.name
=> Alex