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

Here's another way to do it -- put the log file name in a class variable:

require 'singleton'
class MyLogger
  include Singleton
  @@file_name = ""
  def self.file_name= fn
    @@file_name = fn
  end
  def initialize
    @file_name = @@file_name
  end
end

Now you can use it this way:

MyLogger.file_name = "path/to/log/file"
log = MyLogger.instance  # => #

Subsequent calls to instance will return the same object with the path name unchanged, even if you later change the value of the class variable. A nice further touch would be to use another class variable to keep track of whether an instance has already been created, and have the file_name= method raise an exception in that case. You could also have initialize raise an exception if @@file_name has not yet been set.