A array except the indexes are fibonacci numbers!

fibArray.rb

class FibArray
  attr_accessor :array, :cache

  def initialize(array =  [])
    @array = array
    @cache = [1, 2] # put precomputed results as needed    
    generate_next_fib(array.size - cache.size)
  end

  def get(i)
    check_index_error(i)
    array[reverse_fib(i)] 
  end

  def set(i, element)
    check_index_error(i)
    array[reverse_fib(i)] = element
    element
  end

  def push(element)
   generate_next_fib
   array << element
  end

  def pop
    cache.pop
    array.pop
  end

  def remove(i)
    check_index_error(i)
    cache.pop
    array.delete_at(reverse_fib(i))
  end

  def check_index_error(i)
    fib_index = reverse_fib(i)
    raise IndexError if fib_index.nil?
  end

  private
    def fib(fib_i)
      if fib_i >= cache.size 
        cache[fib_i] = fib(fib_i - 1) + fib(fib_i - 2)
      end

      cache[fib_i]
    end

    def generate_next_fib(n = 1)
      n.times { fib(cache.size) }
    end

    def reverse_fib(number)
      cache.index(number)
    end
end

https://www.reddit.com/r/ruby/comments/9xojgm/recursive_and_nonrecursive_fibonacci/e9uesl0/ if you want to see alternative Fibonacci implementations in ruby that can replace fib in the source code.

MIT License