Ruby on Rails: an efficient use of a class in lib/ directory

Question

I've been building a text parser. Ideally, it should be a static class:

keywords = Dictionary.parse(text)

However, the parser (lib/dictionary.rb) has to load some data (for instance, 'stop_words.txt') into memory as an array.

Therefore, as I understand, it can't be a static class, since I need a constructor, which would load that data before the parser can be used.

Then:

lib/dictionary.rb

def initialize
  @stop_words = load_stop_words
end

models/entry.rb

def parse
    @dictionary = Dictionary.new
    self.keywords = @dictionary.parse(self.text)
end

But how inefficient is that? Does it mean, that if I have 1000 entries, the Dictionary class loads 'stop_words.txt' 1000 times, even if the contents of the file are almost constant?

I guess, I am missing something here. There must be a better solution - either without creating multiple instances of the Dictionary class, or by loading data only once, when the application is running.

Answer 1

So your pattern is that you would like a single instance of the object ( which is effectively constant and read-only after instantiation ) which is accessible from many callers but instantiates itself the first time it is called?

The name of this pattern is the Singleton and Ruby has it available as a mixin.

Answer 2

If you are in Rails (as I assume by the tag and the lib directory) then it doesn't get loaded N times: lib files gets loaded only at Rails booting (if you change them, you need to restart the application) and so stop_words will be loaded just one time. Little example ( lib/timenow.rb ):

module Timenow
  @now = Time.now

  def self.doit
    Rails.logger.warn "TIME NOW IS: #{@now}"
  end
end

In any controller, Timenow.doit logs the time this module was loaded.

Answer 3

I would use an initializer, which is stored in config/initializers and those are only loaded on startup, and perfect to load configuration files or setting up stuff. So your Dictionary is under '/lib and in '/config/initializers you create a file called dictionary.rb (or similar, the name is actually not important) which contains the code to load your keywords.