How to set "dynamically" variable values?

Question

I am using Ruby on Rails 3.0.9 and I am trying to set "dynamically" some variable values. That is...

... in my model file I have:

attr_accessor :variable1, :variable2, :variable3   # The 'attributes' argument contains one or more symbols which name is equal to  # one or more of the 'attr_accessor' symbols.  def set_variables(*attributes)    # Here I should set to 'true' all ":variable<N>" attributes passed as symbol   # in the 'attributes' array, but variable names should be interpolated in a    # string.   #    # For example, I should set something like "prefix_#{':variable1'.to_s}_suffix".  end 

How can I set those variable values to true?

---

I tried to use the self.send(...) method, but I did not succeed (but, probably, I don't know how to use at all that send method... is it possible do to that I need by using the send method?!).

Answer 1

attr_accessor :variable1, :variable2, :variable3  def set_variables(*attributes)   attributes.each {|attribute| self.send("#{attribute}=", true)} end 

Answer 2

Here's the benchmark comparison of send vs instance_variable_set:

require 'benchmark'  class Test   VAR_NAME = '@foo'   ATTR_NAME = :foo    attr_accessor ATTR_NAME    def set_by_send i     send("#{ATTR_NAME}=", i)   end    def set_by_instance_variable_set i     instance_variable_set(VAR_NAME, i)   end end  test = Test.new  Benchmark.bm do |x|   x.report('send                 ') do     1_000_000.times do |i|       test.set_by_send i     end   end   x.report('instance_variable_set') do     1_000_000.times do |i|       test.set_by_instance_variable_set i     end   end end 

And the timings are:

      user     system      total        real send                   1.000000   0.020000   1.020000 (  1.025247) instance_variable_set  0.370000   0.000000   0.370000 (  0.377150) 

(measured using 1.9.2)

It should be noted that only in certain situations (like this one, with accessor defined using attr_accessor) are send and instance_variable_set functionally equivalent. If there is some logic in the accessor involved, there would be a difference, and you would have to decide which variant you would need of the two. instance_variable_set just sets the ivar, while send actually executes the accessor method, whatever it does.

Another remark - the two methods behave differently in another aspect: if you instance_variable_set an ivar which doesn't exist yet, it will be created. If you call an accessor which doesn't exist using send, an exception would be raised.