Sieve generated prime finder

prime_finder.rb

class PrimeFinder
  attr_reader :limit, :primes

  def initialize(limit)
    @limit = limit
    @primes = []
    generate_primes!(limit)
  end

  def prime?(candidate)
    sqr_root = Math.sqrt(candidate)
    primes.each do |prime|
      return false if candidate % prime == 0
      break if prime > sqr_root
    end
    true
  end

  def inspect
    "#<PrimeFinder:#{object_id}>"
  end

  private

  def generate_primes!(limit)
    primes.clear
    sieve = [true] * limit
    sieve[0] = sieve[1] = false
    (2..limit).each do |candidate|
      is_candidate_prime = sieve[candidate]
      next unless is_candidate_prime

      primes << candidate
      candidate.step(limit, candidate) do |composite|
        sieve[composite] = false
      end
    end
  end
end

# prime_finder = PrimeFinder.new(1_000_000)
# prime_finder.prime?(999983)
# => true