memoize with memcache store in Rails

memcache_memoize.rb

# Usage:
#
#     module ApplicationHelper
#       extend MemcacheMemoize
#
#       def bar(count = 10)
#         "BAR" * count
#       end
#       memcache_memoize :bar, :expires_in => 10
#     end
#
module MemcacheMemoize
  def memcache_memoize(method, options)
    define_method(:"#{method}_with_memcache_memoize") do |*args|
      key = Digest::SHA1.hexdigest("#{self.class.name}##{method}(#{args.map(&:to_s).join(',')})")
      Rails.cache.fetch(key, options) { __send__(:"#{method}_without_memcache_memoize", *args) }
    end
    alias_method_chain method, :memcache_memoize
  end
end

I've wanted to create this for some time. Glad you posted it and that I found it.

Question:

1. Why the hexdigest? Is that more efficient?