test.rb

#!/usr/bin/env ruby
# frozen_string_literal: true

require 'awesome_print'
require 'active_support/all'
require 'nokul-support'

require 'csv'

source_file = File.expand_path('student_list.csv', ENV['HOME'])
cache_file = source_file + '.dump'

# rubocop:disable Security/MarshalLoad
students = if File.exist? cache_file
             Marshal.load File.read(cache_file)
           else
             CSV.read(source_file, headers: :first_row, encoding: 'bom|utf-8').tap do |array|
               File.write cache_file, Marshal.dump(array)
             end
           end
# rubocop:enable Security/MarshalLoad

ap students.size