If (for whatever reason) I extend Stuff in class Dog how can I access CONST1 through the Dog class? I know I can get CONST1 by saying Stuff::CONST1, but how through dog can I get it. I also know that this code would work if I include Stuff in class Dog.
module Stuff
CONST1 = "Roll Over"
end
class Dog
extend Stuff
end
Dog::CONST1 #NameError: uninitialized constant Dog::CONST1
You're probably thinking of include, not extend.
extend adds the instance methods:
Adds to obj the instance methods from each module given as a parameter.
but include:
Invokes
Module.append_featureson each parameter in reverse order.
and append_features:
Ruby‘s default implementation is to add the constants, methods, and module variables of this module to mod if this module has not already been added to mod or one of its ancestors.
So if you do this:
module M
PANCAKES = 11
end
class C
include M
end
Then you can get PANCAKES from C:
puts C::PANCAKES
# gives you 11
From the documentation of extend:
Adds to obj the instance methods from each module given as a parameter.
It seems there is no reason to expect extend to add the constants.
...but I want the methods to be class methods... what do you mean by this? The methods you add to Stuff WILL be available as class methods to Dog if you extend. On your example, creating a method called test on Stuff will allow you to do Dog.test.extend Stuffthe methods defined in the module Stuff will be class methods to Dog. What I am asking is... I would like to be able to be able use a modules methods as class methods on a given class. To accomplish this you use extend not include as include will make the methods instance methods. But what if there are CONSTANTS in that module that I am extending? It seems logical that I may need to access those CONSTANTS. The only way to access them is to include them.... but I don't want instance methods... I want class methods. Is it possible to access them?Use:
module Stuff
CONST1 = "Roll Over"
end
class Dog
include Stuff
end
Dog::CONST1 # works
See What is the difference between include and extend in Ruby?
