ruby - create singleton with parameters?

Question

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
         


        

Answer 1

This was too long to put into a comment (e.g. stackoverflow said it was too long)

Ok so here's what I came up with:

class MyLogger
  @@singleton__instance__ = nil
  @@singleton__mutex__ = Mutex.new
  def self.config_instance file_name
    return @@singleton__instance__ if @@singleton__instance__
    @@singleton__mutex__.synchronize {
      return @@singleton__instance__ if @@singleton__instance__
      @@singleton__instance__ = new(file_name)
      def self.instance
        @@singleton__instance__
      end
      private_class_method :new
    }
    @@singleton__instance__
  end
  def self.instance
    raise "must call MyLogger.config_instance at least once"
  end
  private
  def initialize file_name
    @file_name = file_name
  end
end

This uses 'config_instance' to create and configure the singleton instance. It redefines the self.instance method once an instance is ready.

It also makes the 'new' class method private after creating the first instance.