Memoist is an extraction of ActiveSupport::Memoizable.

Since June 2011 ActiveSupport::Memoizable has been deprecated. But I love it, and so I plan to keep it alive.

Just extend with the Memoist module

require 'memoist'
class Person
  extend Memoist

  def social_security
    puts "execute!"
    decrypt_social_security
  end
  memoize :social_security
end

person = Person.new

person.social_security
# execute!
# => (returns decrypt_social_security)

person.social_security
# => (returns the memoized value)

And person.social_security will only be calculated once.

Every memoized function (which initially was not accepting any arguments) has a (reload) argument you can pass in to bypass and reset the memoization:

def some_method
  Time.now
end
memoize :some_method

Calling some_method will be memoized, but calling some_method(true) will rememoize each time.

You can even memoize method that takes arguments.

class Person
  def taxes_due(income)
    income * 0.40
  end
  memoize :taxes_due
end

This will only be calculated once per value of income.

You can also memoize class methods.

class Person

  class << self
    extend Memoist
    def with_overdue_taxes
      # ...
    end
    memoize :with_overdue_taxes
  end

end

When a sub-class overrides one of its parent's methods and you need to memoize both. Then you can use the :identifier parameter in order to help Memoist distinguish between the two.

class Clock
  extend Memoist
  def now
     "The time now is #{Time.now.hour} o'clock and #{Time.now.min} minutes"
  end
  memoize :now
end

class AccurateClock < Clock
  extend Memoist
  def now
    "#{super} and #{Time.now.sec} seconds"
  end
  memoize :now, :identifier => :accurate_clock
end

Each memoized function comes with a way to flush the existing value.

person.social_security       # returns the memoized value
person.social_security(true) # bypasses the memoized value and rememoizes it

This also works with a memoized method with arguments

person.taxes_due(100_000)       # returns the memoized value
person.taxes_due(100_000, true) # bypasses the memoized value and rememoizes it

If you want to flush the entire memoization cache for an object

person.flush_cache   # returns an array of flushed memoized methods, e.g. ["social_security", "some_method"]

Everyone who contributed to it in the rails repository.

• Joshua Peek
• Tarmo Tänav
• Jeremy Kemper
• Eugene Pimenov
• Xavier Noria
• Niels Ganser
• Carl Lerche & Yehuda Katz
• jeem
• Jay Pignata
• Damien Mathieu
• José Valim
• Matthew Rudy Jacobs

1. Fork it ( https://github.com/matthewrudy/memoist/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request

Released under the MIT License, just as Ruby on Rails is.