Rspec custom macro like let or let! => pass multiple keys to define array of lets under example group

rspec_custom_macro.rb

module RSpec
  module Core
    module MemoizedHelpers
      module ClassMethods

        # Usage: ways of defining config getters
        # Before:
        # let!(:user_1) { DataSource.get(:user_1) }
        # let!(:user_2) { DataSource.get(:user_2) }
        # After:
        #   keys = [:user_1, :user_2]
        #   let_config_list!(keys)
        def let_config_list!(keys, &block)
          unless block_given?
            block =  ->(key) { OtherSource.get(key) }
          end
          running_example= caller[0]
          keys.each do |key|
            MemoizedHelpers.module_for(self).send(:define_method, key, -> {
              running_example.instance_variable_get("@#{key}") ||
                running_example.instance_variable_set("@#{key}", block.call(key))
            })
            before(:all) { __send__(key) }
          end
        end
      end
    end
  end
end