A dead simple memoize library for Ruby

memoist.rb

# There are many fancier memoize libraries out there:
# https://github.com/tycooon/memery
# https://github.com/makandra/memoized

# Some of them support expiration, some memoizing methods with arguments.
# However, I just want a dead simple implementation that memoizes getters only.

module Memoist
  def memoize name
    if instance_method(name).arity != 0
      raise "Only methods without arguments are supported by `memoize`."
    else
      @_memoist_module ||= begin
        mod = Module.new
        prepend mod
        mod
      end
      key = "@_memoized_#{name}".to_sym
      @_memoist_module.define_method(name) do
        if instance_variable_defined?(key)
          instance_variable_get(key)
        else
          instance_variable_set(key, super())
        end
      end
    end
  end
end

Class.include Memoist

# In memory of Matthew Rudy Jacobs who built the original memoist library:
# https://github.com/matthewrudy/memoist