active_attr_attribute_memoize.rb

require "active_attr"
require "memoist"

class Model
  include ActiveAttr::Model
  extend Memoist

  # by default ActiveAttr calls typecaster every time attribute reader is called
  # this patch adds memoization
  # https://github.com/cgriego/active_attr/blob/v0.8.5/lib/active_attr/attributes.rb#L199
  def self.attribute!(name, options={})
    attribute_definition = super
    send(:memoize, attribute_definition.name)

    define_method("#{attribute_definition.name}=") do |value|
      result = super(value)
      flush_cache(attribute_definition.name)
      result
    end

    attribute_definition
  end

  attribute :number, typecaster: proc { |value| value * Time.now.to_f * 1000 }
end

require "minitest/autorun"
require "pry"

describe Model do
  it "flushes cache on writer" do
    m = Model.new(number: 1)
    
    number1 = m.number
    number1.wont_be_nil
    m.number.must_equal number1
    
    m.number = 5
    number2 = m.number
    number2.wont_be_nil
    m.number.must_equal number2
    number2.wont_equal number1
  end
end