Memoization to memcache

memoizable_with_mc.rb

# Memcache wrapping in a declarative fashion.
#
# Usage example:
#
#   class << self
#     extend Utils::MemoizableWithMC
#
#     def get_host_details(id)
#       select('host_first_name, host_last_name, host_email').find(id)
#     end
#     memoize_with_mc :get_host_details, :expires_in => 10
#
#   end
#
# Limitations:
#   - The MC key uses arg.inspect
#   - For the MC options (like :expires_in => 10), it must be possible to
#     inspect and then eval the object, and get a copy of the original object.
# 

module Utils
  module MemoizableWithMC

    def self.wrapper(key, options = {})
      Rails.cache.fetch(key, options) { yield }
    end

    def memoize_with_mc(symbol, options = {})
      original_method = :"_unmemoized_with_mc_#{symbol}"

      class_eval <<-EOS, __FILE__, __LINE__ + 1
        alias #{original_method} #{symbol}

        define_method(symbol) do |arg|
          MemoizableWithMC::wrapper("MWMC:#{symbol}:" + arg.inspect, eval("#{options.inspect}")) do
            #{original_method}(arg)
          end
        end
      EOS
    end

  end
end