Store and retrieve variables from objects

Question

I want to store and retrieve some variables from object. For example in a

a = "a"

So far I found two possible ways to do it.

• Using instance_variable_set and instance_variable_get

  a.instance_variable_set(:@x, 10)
  a.instance_variable_get(:@x) # => 10
  

• or just using instance_eval

  a.instance_eval { @y = 5 }
  a.instance_eval { @y } # => 5
  

The second approach looks shorter and simpler for me, is there anything wrong with my code if I prefer this one?

Answer 1

Speed isn't everything, but... the instance_variable_set method is faster than using instance_eval. Here's a benchmark if you're interested: https://gist.github.com/1268188

Here's another post that gives another good reason for avoiding instance_eval when possible: Alex Kliuchnikau on instance_eval

Answer 2

If there is no good reason (e.g. metaprogramming), you'd better avoid using instance_variable_get(set), coz it will break encapsulation. You can refer to ruby-doc: thereby frustrating the efforts of the class’s author to attempt to provide proper encapsulation.

And the best practice of using instance_eval is to compose DSL style:

assume you have a Engineer class with instance method: program, play and sleep. So,

sb = Engineer.new

sb.program
sb.play
sb.sleep

# is equivalent to
sb.instance_eval do
  program
  play
  sleep
end

In this case, it's shorter :)