attribute_readers.rb

module AttributeReaders
  class <<self
    # str = "foo"
    # overrides = {
    #   another_reverse: :reverse,
    #   exclaimed: ->(str) { str + "!" },
    #   to_sym: ->(str) { str.reverse.to_sym }
    # }
    # reader = AttributeReaders.object_reader(str, overrides)
    # [:reverse, :another_reverse, :exclaimed, :to_sym].map(&reader)
    # => ["oof", "oof", "foo!", :oof]
    def object_reader(object, overrides=nil)
      ->(key) { (overrides && overrides[key] || key).to_proc.(object) }
    end

    # user = {id: 99, name: "James"}
    # overrides = {
    #   another_id: :id,
    #   name: ->(user) { user[:name].upcase }
    # }
    # reader = AttributeReaders.hash_reader(user, overrides)
    # [:id, :another_id, :name, :not_a_key].map(&reader)
    # => [99, 99, "JAMES", nil]
    def hash_reader(hash, overrides=nil)
      ->(key) { hash_proc_from(overrides && overrides[key] || key).(hash) }
    end

  private

    def hash_proc_from(x)
      x.is_a?(Proc) ? x : ->(hash) { hash[x] }
    end
  end
end