Warmup solution

resurrect_eratosthenes.rb

class Sieve
  attr_reader :unmarked, :primes

  def initialize(max)
    @unmarked = (2..max).to_a
    @primes = []

    resurrect_eratosthenes
  end

  def resurrect_eratosthenes
    until unmarked.empty? do
      prime = unmarked.shift

      primes << prime
      delete_multiples(prime)
    end
  end

  def delete_multiples(prime)
    unmarked.delete_if { |number| number % prime == 0 }
  end
end