Cached Attributes

cached_attrs.rb

module CachedAttrs
  def self.build_cache_variable_name(attr_name)
    "@_cached_#{attr_name}".to_sym
  end

  def self.extended(mod)
    mod.send(:include, CachedAttrs::InstanceMethods)
  end

  def cached_attr(attr_name, &block)
    cache_variable_name = CachedAttrs.build_cache_variable_name(attr_name)

    define_method attr_name do
      return instance_variable_get cache_variable_name if instance_variable_defined? cache_variable_name

      cached_value = instance_eval &block
      instance_variable_set cache_variable_name, cached_value
      cached_value
    end
  end

  module InstanceMethods
    def clear_cached_attr(attr_name)
      remove_instance_variable CachedAttrs.build_cache_variable_name(attr_name)
    end

    def set_cached_attr(attr_name, value)
      instance_variable_set CachedAttrs.build_cache_variable_name(attr_name), value
    end
  end
end