Push element to dynamic array (created with instance_variable_set) in Rails

Question

I have a list of attributes. Each attribute will be setted as an empty array and i want to push elements to each array.

I figured out how to create a dynamic array with instance_variable_set but i couldn't push elements to it.

That's what i did:

attributes = ["eye","hair_color","hair_size","hair_type"]
i = 0
attributes.each do |a|
    # Dynamic arrays are created, like: @eye = []
    instance_variable_set("@#{a}", [])
    # My attempt to push element
    "@#{a}".push(i)
    i += 1
end

How can i push an element to those dynamic arrays?

Peter Balaban · Accepted Answer · 2017-10-23 19:22:52Z

2

instance_variable_get("@#{a}").push(i) will work

answered Oct 23, 2017 at 19:22

Peter Balaban

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jvillian · Accepted Answer · 2017-10-23 19:25:41Z

1

Petr Balaban has it right. I thought I would also note that you can do each_with_index instead of setting and incrementing i manually:

attributes = ["eye","hair_color","hair_size","hair_type"]

attributes.each_with_index do |a,i|
  # Dynamic arrays are created, like: @eye = []
  instance_variable_set("@#{a}", [])
  # As Petr noted...
  instance_variable_get("@#{a}").push(i)
end

answered Oct 23, 2017 at 19:25

jvillian

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Comments

Aleksei Matiushkin · Accepted Answer · 2017-10-23 19:36:24Z

1

Another approach would be:

attributes = %w|eye hair_color hair_size hair_type|
attributes.each_with_index do |a, idx|
  self.class.send :attr_accessor, a.to_sym
  public_send "#{a}=", idx
  (public_send a) << idx
end

Now you have an access to these variables by getter:

hair_size
#⇒ 2

answered Oct 23, 2017 at 19:36

Aleksei Matiushkin

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