How can I mix in Singleton to create a class that accepts initialization parameters?

I've seen how to define a class as being a singleton (how to create a singleton in Ruby):

require 'singleton'
 
class Example
  include Singleton
end

But what if I want to pass some parameters to #new when initializing that single instance? Example should always have certain properties initialized. For example, say I had a class whose sole purpose is to log to a file but it requires a name of a file to log to before it can work.

class MyLogger
  def initialize(file_name)
    @file_name = file_name
  end
end

How can I make MyLogger a singleton but make sure it gets a file_name?

Singleton does not provide this functionality, but instead of using singleton you could write it by yourself

class MyLogger
  @@singleton__instance__ = nil
  @@singleton__mutex__    = Mutex.new

  def self.instance(file_name)
    return @@singleton__instance__ if @@singleton__instance__

    @@singleton__mutex__.synchronize do
      return @@singleton__instance__ if @@singleton__instance__

      @@singleton__instance__ = new(file_name)
    end
    @@singleton__instance__
  end

  private

  def initialize(file_name)
    @file_name = file_name
  end
  private_class_method :new
end

It should work, but I did not tested the code.

This code forces you to use MyLogger.instance <file_name> or at least at the first call if you know it will be first time calling.