#137 Memoization (revised)

Aug 18, 2012 | 9 minutes | Performance, Caching

Memoization is a convenient way to cache a method's response. Here I show several ways to accomplish this from scratch since the ActiveSupport::Memoizable module has been deprecated.

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Memoist

          terminal
        
irb -w
@a || @a = "foo"
@b ||= "bar"
a || a = "foo"
b ||= "bar"

          models/product.rb
        
class Product < ActiveRecord::Base
  def filesize(*args)
    @filesize ||= {}
    @filesize[args] ||= calculate_filesize(*args)
  end

private

  def calculate_filesize(num = 1)
    sleep 0.5
    4815162342 * num
  end

  # Alternative approaches
  #
  # def filesize
  #   @filesize = calculate_filesize unless defined? @filesize
  #   @filesize
  # end
  #
  # ---
  #
  # def filesize(*args)
  #   @filesize ||= Hash.new do |hash, key|
  #     hash[key] = calculate_filesize(*key)
  #   end
  #   @filesize[args]
  # end
  # 
  # ---
  #
  # def self.memoize(name)
  #   alias_method "_unmemoized_#{name}", name
  #   define_method(name) do |*args|
  #     @_memoized ||= {}
  #     @_memoized[name] ||= Hash.new do |hash, key|
  #       hash[key] = send("_unmemoized_#{name}", *key)
  #     end
  #     @_memoized[name][args]
  #   end
  # end
  # 
  # def filesize(num = 1)
  #   sleep 0.5
  #   4815162342 * num
  # end
  # memoize :filesize
end