Memoist

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.

Usage

Just extend with the Memoist module

“by 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:

“by 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.

“by 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.

“by 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.

“by 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

“

Reload

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

“by 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

“by 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

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

“

Authors

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

Contributing

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

License

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