Memery

Memery is a Ruby gem that simplifies memoization of method return values. In Ruby, memoization typically looks like this:

def user
  @user ||= User.find(some_id)
end

However, this approach fails if the calculated result can be nil or false, or if the method uses arguments. Additionally, multi-line methods require extra begin/end blocks:

def user
  @user ||= begin
    some_id = calculate_id
    klass = calculate_klass
    klass.find(some_id)
  end
end

To handle these situations, memoization gems like Memery exist. The example above can be rewritten using Memery as follows:

memoize def user
  some_id = calculate_id
  klass = calculate_klass
  klass.find(some_id)
end

Installation

Add gem "memery" to your Gemfile.

Usage

class A
  include Memery

  memoize def call
    puts "calculating"
    42
  end

  # Alternatively:
  # def call
  #   ...
  # end
  # memoize :call
end

a = A.new
a.call # => 42
a.call # => 42
a.call # => 42
# "calculating" will only be printed once.

a.call { 1 } # => 42
# "calculating" will be printed again because passing a block disables memoization.

Memoization works with methods that take arguments. The memoization is based on these arguments using an internal hash, so the following will work as expected:

class A
  include Memery

  memoize def call(arg1, arg2)
    puts "calculating"
    arg1 + arg2
  end
end

a = A.new
a.call(1, 5) # => 6
a.call(2, 15) # => 17
a.call(1, 5) # => 6
# "calculating" will be printed twice, once for each unique argument list.

For class methods:

class B
  class << self
    include Memery

    memoize def call
      puts "calculating"
      42
    end
  end
end

B.call # => 42
B.call # => 42
B.call # => 42
# "calculating" will only be printed once.

Conditional Memoization

class A
  include Memery

  attr_accessor :environment

  def call
    puts "calculating"
    42
  end

  memoize :call, condition: -> { environment == 'production' }
end

a = A.new
a.environment = 'development'
a.call # => 42
# calculating
a.call # => 42
# calculating
a.call # => 42
# calculating
# Text will be printed every time because result of condition block is `false`.

a.environment = 'production'
a.call # => 42
# calculating
a.call # => 42
a.call # => 42
# Text will be printed only once because there is memoization
# with `true` result of condition block.

Memoization with Time-to-Live (TTL)

class A
  include Memery

  def call
    puts "calculating"
    42
  end

  memoize :call, ttl: 3 # seconds
end

a = A.new
a.call # => 42
# calculating
a.call # => 42
a.call # => 42
# Text will be printed again only after 3 seconds of time-to-live.
# 3 seconds later...
a.call # => 42
# calculating
a.call # => 42
a.call # => 42
# another 3 seconds later...
a.call # => 42
# calculating
a.call # => 42
a.call # => 42

Checking if a Method is Memoized

class A
  include Memery

  memoize def call
    puts "calculating"
    42
  end

  def execute
    puts "non-memoized"
  end
end

a = A.new

a.memoized?(:call) # => true
a.memoized?(:execute) # => false

Differences from Other Gems

Memery is similar to Memoist, but it doesn't override methods. Instead, it uses Ruby 2's Module.prepend feature. This approach is cleaner, allowing you to inspect the original method body with method(:x).super_method.source, and it ensures that subclasses' methods function properly. If you redefine a memoized method in a subclass, it won't be memoized by default. You can memoize it normally without needing an awkward identifier: argument, and it will just work:

class A
  include Memery

  memoize def x(param)
    param
  end
end

class B < A
  memoize def x(param)
    super(2) * param
  end
end

b = B.new
b.x(1) # => 2
b.x(2) # => 4
b.x(3) # => 6

b.instance_variable_get(:@_memery_memoized_values)
# => {:x_70318201388120=>{[1]=>2, [2]=>4, [3]=>6}, :x_70318184636620=>{[2]=>2}}

Note how both methods' return values are cached separately without interfering with each other.

Another key difference is that Memery doesn't change the method's signature (no extra reload parameter). If you need an unmemoized result, simply create an unmemoized version of the method:

memoize def users
  get_users
end

def get_users
  # ...
end

Alternatively, you can clear the entire instance's cache:

a.clear_memery_cache!

You can also provide a block, though this approach is somewhat hacky:

a.users {}

Object Shape Optimization

In Ruby 3.2, a new optimization called "object shape" was introduced, which can have negative interactions with dynamically added instance variables. Memery minimizes this impact by introducing only one new instance variable after initialization (@_memery_memoized_values). If you need to ensure a specific object shape, you can call clear_memery_cache! in your initializer to set the instance variable ahead of time.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/tycooon/memery.

License

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

Author

Created by Yuri Smirnov.