primer.rb

require 'prime'

class Primer < Prime::EratosthenesSieve
  def self.call(limit)
    new.call(limit)
  end

  def call(limit)
    (1..limit).to_a.inject([]) do |arr, n|
      arr << get_nth_prime(n)
      arr
    end
  end

  def get_nth_prime(n)
    super
  end
end

Returns the first n prime numbers. Exercise to expose the private instance method Prime::EratosthenesSieve#get_nth_prime(n) by subclassing.