How can I initialize a module's instance variables in Ruby?

Question

I have some modules where I would like to use instance variables in. I'm currently initializing them like this:

module MyModule   def self.method_a(param)     @var ||= 0     # other logic goes here   end end 

I also could call a init method to initialize them:

def init   @var = 0 end 

but this would mean I have to remember to always call it.

Is there a better way of doing this?

Answer 1

Initialize them in the module definition.

module MyModule   # self here is MyModule   @species = "frog"   @color = "red polka-dotted"   @log = []    def self.log(msg)     # self here is still MyModule, so the instance variables are still available     @log << msg   end   def self.show_log     puts @log.map { |m| "A #@color #@species says #{m.inspect}" }   end end  MyModule.log "I like cheese." MyModule.log "There's no mop!" MyModule.show_log #=> A red polka-dotted frog says "I like cheese."                   #   A red polka-dotted frog says "There's no mop!" 

This will set the instance variables when the module is defined. Remember, you can alwasys reopen the module later to add more instance variables and method definitions, or to redefine existing ones:

# continued from above... module MyModule   @verb = "shouts"   def self.show_log     puts @log.map { |m| "A #@color #@species #@verb #{m.inspect}" }   end end MyModule.log "What's going on?" MyModule.show_log #=> A red polka-dotted frog shouts "I like cheese."                   #   A red polka-dotted frog shouts "There's no mop!"                   #   A red polka-dotted frog shouts "What's going on?" 

Answer 2

You can use:

def init(var=0)  @var = var end 

And it will default to 0 if you don't pass anything.

If you don't want to have to call it everytime, you could use something like this:

module AppConfiguration    mattr_accessor :google_api_key    self.google_api_key = "123456789" ...  end