I'm confused about these two class when I was reading Module document. First of all, I saw there is a way to set the named constant to the given object.
Object.const_set("FOO", 40)
But I check ruby doc, there is no const_set in Object method, then I found out it was defined in Module.
I thought Object is the default root of all Ruby objects. Why it can use module method? I am confused about the relationship between those.
As shown below :const_set is an instance method stored in Module:
Module.instance_methods(false).include? :const_set #=> true
Also note that Object is an instance of Class:
Object.instance_of? Class #=> true
And Class is a subclass of Module:
Class.superclass #=> Module
All of this means that instance methods defined within Module are available to Class objects via inheritance. So any instance of Class (such as Object) has at its disposal all the instance methods (including :const_set) stored in Module.
In ruby, basically every class is an instance of the Class class and every class is a subclass of Object. And both Object and Class are classes. If you do
Object.is_a?class
Class.is_a?class
In both cases, you will get a true value. Class has Module as one of the ancestor, therefore, you can use
Object.const_set("FOO", 40)
There is also #ancestors to give you some more context on the object model.
> Module.ancestors
=> [Module, Object, PP::ObjectMixin, Kernel, BasicObject]
'Hello'.upcase, where would you look for theupcasemethod … in the string'Hello'or in its class (String) and its superclasses? Now, if you callObject.const_set, where would you look for theconst_setmethod … in the classObjector in its class (Class) and its superclasses?