A Ruby Memoization Helper
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Memist is a tiny library to help with memoizing values in Ruby classes. There are many other memoization libraries around but Memist provides more invalidation than others. Let's jump right into a demonstration.

class Person

  attr_accessor :first_name, :last_name, :date_of_birth

  def age
  memoize :age, :uses => [:date_of_birth]


Here you can see we have a method called age which generates a person's age based on on their date_of_birth. It returns an integer. Each time we run this method, we don't want to go to the extra power of calcuating the age, so we want to cache the value for this instance. To do this, we just add the memoize method to our object.

person = Person.new
person.date_of_birth = Date.new(1986, 6, 10)
person.age      #=> 29 (retrieved by calculation)
person.age      #=> 29 (retrieved from the cache based)

Unlike other libraries, Memist can also ensure that the cached value is cleared whenever dependent fields are changed. In this example, when the date of birth is changed, the age should also be re-calculated.

person = Person.new
person.date_of_birth = Date.new(1986,6, 10)
person.age  #=> 29
person.age  #=> 29 (from cache)
person.date_of_birth = Date.new(1985, 6, 10)
person.age  #=> 30
person.age  #=> 30 (from cache)


Simple. Just add the gem to your Gemfile and we'll handle the rest. Memist works with any Ruby Object and has special support to handle Active Record classes too.

gem 'memist', '~> 1.0'


You need to specify which fields you want to be memoized in your objects. You do this by calling memoize as shown above.

You can optionally provide an array of attributes as a :uses option. This will ensure that the cached value is cleared when any of these attributes are cleared. You can also specify other memozied methods in this array and their attributes will be cleared too.

Other handy methods

person = Person.new
person.date_of_birth = Date.new(1986, 6, 10)

# Access the raw underlying without any memoization
person.age_without_memoization    #=> 29

# Clear the cache for all methods on the model

# Clear the cache for a single method on the model

# Find out of a vale is memoized or not? When the value has been returned from
# memoized cache, it will be true otherwise it will be false.
person.age.memoized?    #=> false
person.age.memoized?    #=> true