Memo::It

Clever memoization helper that uses Ruby internals instead of meta-programming.

Using Memo::It

Basic Usage

Requiring the gem will add a memo method to the Object class so that you can just use it like so:

  def load_stuff_from_the_web
    memo do
      # some expensive operation like HTTP request
      # the return value of the block will be memoized
      HTTPClient.get('https://github.com/phoet/memo-it')
    end
  end

Instance vs Class memoization

Per default, the memoization will be done on an instance level, so every instance of an object will have it's own memoization namespace:

  class Loader
    def initialize(url)
      @url = url
    end

    def content
      memo do
        # fetch the url content from the web
      end
    end
  end

  issues_loader = Loader.new('https://github.com/phoet/memo-it/issues')
  pulls_loader  = Loader.new('https://github.com/phoet/memo-it/pulls')

  issues_loader.content # load & memoize the issues
  pulls_loader.content # load & memoize the pulls

But you can also memoize on a global/class scope. This is needed if you want to use Memo::It in dynamically instanciated objects like Rails helpers:

  module WebHelper
    def content(url)
      Memo::It.memo do
        # fetch the url content from the web
      end
    end
  end

Parameters as scopes

In case you want to memoize something that has parameters, Memo::It will just use all local variables in scope to determine the memoization:

  def load_repo(name = 'memo-it')
    memo do
      # in this case the result will be memoized per name
      HTTPClient.get("https://github.com/phoet/#{name}")
    end
  end

If, on the other hand, you want to memoize parameters but ignore one of them, you can do this by adding it to the :except list:

  def load_repo(name = 'memo-it', time = Time.now)
    memo(except: :time) do
      # in this case the result will be memoized per name
      HTTPClient.get("https://github.com/phoet/#{name}?time=#{time}")
    end
  end

Or provide a list of parameters to except:

  def load_repo(name = 'memo-it', time = Time.now, other = 'irrelevant')
    memo(except: [:time, :other]) do
      # in this case the result will be memoized per name
      HTTPClient.get("https://github.com/phoet/#{name}?time=#{time}&other=#{other}")
    end
  end

To be symmetric, it's also possible to define one or more parameters through the :only key:

  def load_repo(name = 'memo-it', time = Time.now, format = 'json')
    memo(only: [:name, :format]) do
      # in this case the result will be memoized per name & format
      HTTPClient.get("https://github.com/phoet/#{name}?time=#{time}&format=#{format}")
    end
  end

Provide your own memoization keys through the :provided key:

  def load_repo(name = 'memo-it')
    memo(provided: Date.today.day_of_week) do
      # in this case the result will be memoized per name and day_of_week
      HTTPClient.get("https://github.com/phoet/#{name}")
    end
  end

Turning it on and off

In case you would like to disable memoization (ie. for testing) you can disable Memo::It:

  # enabled is default
  Memo.enabled? # => true

  # disable memoization globally
  Memo.disable
  Memo.enabled? # => false

  # re-enable memoization
  Memo.enable
  Memo.enabled? # => true

Caveats

Multiple calls to memo on the same line of code

If you want to call memo twice within the same line of code, you would need provide a custom key through the :provided argument. This is not recommended through. A better alternative would be to put both calls into their own sub-methods and call those instead.

Runtime-Speed

Compared to other memoization frameworks, the memo method requires more computation and is slower by size of a magnitude: #6 Do not use this library to optimize hot code-paths! Use it to cache really slow things such as network-requests or generation of large strings like JSON objects etc. Whatever you do, benchmark your code in order to see if the memoization strategy you use is a good fit for your use-case.

Installation

As a Gem

Add this line to your application's Gemfile:

gem 'memo-it'

And then execute:

$ bundle

Or install it yourself as:

$ gem install memo-it

Copy & Paste

If you don't want to include yet another Gem, just run this in your shell:

$ /usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/phoet/memo-it/master/bin/install)"

Changelog

See CHANGELOG.md.

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/phoet/memo-it. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

License

The gem is available as open source under the terms of the MIT License.