[instance_eval and Procs] Using instance_eval and code blocks

generate_method.rb

# Will experience a performance benefit over #instance_eval as
# this method will experience only 1 scope change whereas with
# #instance_eval, that will happen for each request
def generate_method(method_name, &block)
  method_name = method_name.to_sym
  define_method(method_name, &block)
  # grab the unbound method block
  method = instance_method method_name
  remove_method method_name
  method
end

instance_eval_demo.rb

a = [1,2,3,4,5]
block = proc { size }
a.instance_eval(&block) #=> 5