A module is like a named "wrapper" around a set of methods, constants, and classes.
The various of code inside the module share the same "namespace".
And they are all visible to each other but are not visible to code outside the module.
Ruby class library defines a number of modules such as Math and Kernel.
Math module contains mathematical methods such as sqrt to return a square route and constants such as PI.
The Kernel module contains methods such as print, puts, and gets.
Let's assume you have written this module:
module MyModule
GOODMOOD = "happy"
BADMOOD = "grumpy"
def greet
return "I'm #{GOODMOOD}. How are you?"
end
def MyModule.greet
return "I'm #{BADMOOD}. How are you?"
end
end
To call a module method, use
MyModule.greet
To access the module constants, using ::
puts(MyModule::GOODMOOD) #=> happy
To access the module instance method, use mixins.