Double Colon
The :: (double colon) syntax is used to define a namespace or reference a namespace. It can also be used to call a method.
Module Namespacing
We can define a namespace for our modules, classes, and constants through nesting.
MY_CONSTANT = "Outer Space"
module OuterModule
module InnerModule
class MyClass
MY_CONSTANT = "World"
def self.hello
puts "Hello, #{MY_CONSTANT}"
puts "Hello, #{::MY_CONSTANT}"
puts ancestors
end
end
end
end
OuterModule::InnerModule::MyClass.hello
puts OuterModule::InnerModule::MyClass::MY_CONSTANT
A couple things to note in this code block:
- Once defined, we can traverse the namespace chain to call a method —
OuterModule::InnerModule::MyClass.hello - In the same way, we can traverse it to reference a constant —
OuterModule::InnerModule::MyClass::MY_CONSTANT - If there a global entity that we are trying to reference outside the current namespace that conflicts, we can escape the namespace with a leading double-colon —
::MY_CONSTANT
As long as a module already exists, we can use it to define a namespaced entity.
module OverHere
end
class OverHere::MyClass
def self.hello
puts ancestors
end
end
Calling A Method
Oddly enough, we can call a method with :: instead of the typical .. I wouldn't recommend doing this in any actualy code though.
> 'html'::upcase
=> "HTML"