From: James Edward Gray II <james@...>
Date: 2005-10-07T11:47:41+09:00
Subject: Re: is there a way to add attributes to instances?

On Oct 6, 2005, at 9:36 PM, ako... wrote:

> hello,
>
> is there a way to add properties to instances and access them later
> just like if they were defined in the object's class?
>
>
> a.newproperty = 123
> puts a.newproperty
>
> i know how to dynamically add newproperty to the class of instance  
> 'a',
> but is there a way to do it per instance? or do i have to maintain an
> explicit hash table on my objects and access these attributes through
> the table?

Here's two different ideas to get you going:

irb(main):001:0> require "ostruct"
=> true
irb(main):002:0> a = OpenStruct.new
=> <OpenStruct>
irb(main):003:0> a.new_property = 123
=> 123
irb(main):004:0> a.property
=> nil

irb(main):018:0> class Magic
irb(main):019:1>   def method_missing( meth, *args, &block )
irb(main):020:2>     if meth.to_s =~ /^(\w+)=$/
irb(main):021:3>       instance_variable_set("@#{$1}", *args)
irb(main):022:3>     elsif instance_variables.include? "@#{meth}"
irb(main):023:3>       instance_variable_get("@#{meth}")
irb(main):024:3>     else
irb(main):025:3*       super
irb(main):026:3>     end
irb(main):027:2>   end
irb(main):028:1> end
=> nil
irb(main):029:0> b = Magic.new
=> #<Magic:0x1b0764>
irb(main):030:0> b.new_property = 123
=> 123
irb(main):031:0> b.new_property
=> 123

Hope that helps.

James Edward Gray II