HashCache.rb

# Example simple stupid in-memory cache
class HashCache
  def initialize(seconds_timeout)
    @seconds_timeout = seconds_timeout
    @cache = {}
  end
  def fetch(key, &block)
    if @cache[key] && fresh?(@cache[key][:set_at])
      return @cache[key][:value]
    else
      value = yield
      @cache[key] = {:value => value, :set_at => Time.now}
      return value
    end
  end
  def fresh?(set_at)
    (set_at + @seconds_timeout) > Time.now
  end
end

CACHE = HashCache.new(5) # 5 seconds

def fetch_photos(tags)
  puts "Fetching photos for #{tags.inspect}"
  CACHE.fetch(tags) { puts "Doing API call..."; sleep(1); ["photo.jpg"] }
end

tags = %w(lachlanhardy espresso martini)

fetch_photos(tags)
fetch_photos(tags)
fetch_photos(tags)
fetch_photos(tags)
fetch_photos(tags)

puts "No request for 8 seconds"
sleep(8)

fetch_photos(tags)
fetch_photos(tags)
fetch_photos(tags)
fetch_photos(tags)
fetch_photos(tags)