Essentially I'm wondering how to place callbacks on objects in ruby, so that when an object is changed in anyway I can automatically trigger other changes:

class MyClass
  attr_reader :proxy
  def proxy=(string_proxy = "")
    begin
      @proxy = URI.parse("http://"+((string_proxy.empty?) ? ENV['HTTP_PROXY'] : string_proxy))
      @http = Net::HTTP::Proxy.new(@proxy.host,@proxy.port)
    rescue
      @http = Net::HTTP
    end
  end
end

m = MyClass.new
m.proxy = "myproxy.com:8080"
p m.proxy
# => <URI: @host="myproxy.com" @port=8080>
# However changing m.proxy will not change the @http variable, as proxy= is not being called.

# Desired functionality:
m.proxy = nil
# Now @http.class is Net::HTTP, not Net::HTTP::Proxy