Ruby LRU Cache

class LRUCache
 
  def initialize(size = 10)
    @size = size
    @store = {}
    @lru = []
  end
 
  def set(key, value)
    @store[key] = value
    set_lru(key)
    @store.delete(@lru.pop) if @lru.size > @size
  end
 
  def get(key)
    set_lru(key)
    @store[key]
  end
 
  private
    def set_lru(key)
      @lru.unshift(@lru.delete(key) || key)
    end
end
 
 
if __FILE__ == $0
  require 'test/unit'
 
  class TestLRUCache < Test::Unit::TestCase
 
    def setup
      @cache = LRUCache.new(2)
    end
 
    def test_last_droped
      @cache.set(:a, 'a')
      @cache.set(:b, 'b')
      @cache.set(:c, 'c')
 
      assert_nil @cache.get(:a)
      assert_equal 'b', @cache.get(:b)
      assert_equal 'c', @cache.get(:c)
    end
 
    def test_get_keeps_key
      @cache.set(:a, 'a')
      @cache.set(:b, 'b')
      @cache.get(:a)
      @cache.set(:c, 'c')
 
      assert_equal 'a', @cache.get(:a)
      assert_nil @cache.get(:b)
      assert_equal 'c', @cache.get(:c)
    end
 
    def test_set_keeps_key
      @cache.set(:a, 'a')
      @cache.set(:b, 'b')
      @cache.set(:a, 'a')
      @cache.set(:c, 'c')
 
      assert_equal 'a', @cache.get(:a)
      assert_nil @cache.get(:b)
      assert_equal 'c', @cache.get(:c)
    end
  end
end