Dynamic config

gistfile1.rb

# I was considering how I might want to further implement my gem and incorporate configuration settings for it.  I wanted only one instance of my configuration and it needed to be part of my module.  So I’ve come up with a solution I like that allows me to do this and even have a true “sense” of untouchable constants.

# I’ve found OpenStruct to be for my liking in this situation as it allows for any configuration (variable) to be set on it.  I’ve also found I can set “unalterable” variables… at least through standard assignment options.


# The reason I created the class MyProject::MyConfig just to inherit OpenStruct is that I want my configuration to be identified by a class name that indicates it is a config object that belongs to my project.  In module MyProject I use attr_reader for config because we are getting the OpenStruct instance handed back to us and we can still invoke method/value assignment on it.  I use the single class variable @config for the internal singleton value because it’s not going anywhere (No need to use @@config).  The method config is defined on the singleton instance of the module MyProject via the class << self.  So to set any value all I need to do is MyProject.config.new_value = 42.


require 'ostruct'

class MyProject::MyConfig < OpenStruct
end

module MyProject
  attr_reader :config
  class << self
    def config
      @config ||= MyConfig.new
    end
  end
end


# EDITABLE

MyProject.config.new_value = 42
MyProject.config.new_value
# => 42

MyProject.config.hair = :awesome
MyProject.config.hair
# => :awesome

MyProject.config.hair = :bad_hair_day
MyProject.config.hair
# => :bad_hair_day


# If I want to set a constant value that I don’t want to change then all I have to do is define the method within the OpenStruct instance.  You can do it in the class, or open it up with the singleton opener.

class MyProject::MyConfig < OpenStruct
  def no_touchy
    :always_this
  end
end
x = MyProject::MyConfig.new
x.no_touchy
# => :always_this
x.no_touchy = 493872
x.no_touchy
# => :always_this

class << x
  def also_no_touchy
    :cant_touch_this
  end
end
x.also_no_touchy
# => :cant_touch_this
x.also_no_touchy = :batman
x.also_no_touchy
# => :cant_touch_this

# If you want a default value that can be updated; then you may implement that method with a method_missing(:method_name) || :value .  As soon as you assign a new value it will choose the updated value.


class MyProject::MyConfig < OpenStruct
  def no_touchy
    :always_this
  end
end
x = MyProject::MyConfig.new
x.no_touchy
# => :always_this
x.no_touchy = 493872
x.no_touchy
# => :always_this

class << x
  def also_no_touchy
    :cant_touch_this
  end
end
x.also_no_touchy
# => :cant_touch_this
x.also_no_touchy = :batman
x.also_no_touchy
# => :cant_touch_this