Modules in Ruby

A deeper dive than usual

Hal Fulton

June 3, 2019

I wrote one of these books

A module is...

A tool for namespacing
A container for methods and constants
Like a class, but not

A module is
not a class...

Can't be instantiated
Has no
Has no instance variables (of its own)

initialize

What can we do

with a module?

"nothing" (namespacing)
```
include
```
```
extend
```
```
prepend
```

Namespacing

```
Math::PI
```
```
Math::sin
```
```
Math.sin
```
```
ThisClass::SomeModule
```
```
ThisModule::OtherClass
```
```
A::B:C::D::Constant
```
```
A::B::C::D::method
```
```
A::B::C::D.method
```

"Partial" Multiple Inheritance?

class Asian
end

module Mormon
end

class RubyInventor < Asian
  include Mormon
end

p RubyInventor.ancestors   
# [RubyInventor, Mormon, Asian, Object, Kernel, BasicObject]

matz = RubyInventor.new
p matz.is_a? Asian          # true
p matz.is_a? Mormon         # true

Some core modules

```
Comparable           <=>
```

```
Enumerable           each
 
```

depends on
being implemented

depends on

```
Forwardable
```
```
Math
```

include

extend

prepend

Manipulating Modules

Copy all constants/methods into a context
(methods go to "current" level)

Copy all constants/methods (methods go in as singletons) -- most commonly used to create class methods

Copy all constants/methods -- methods are given *precedence* over the class's own instance methods!

The Superman example...

ancestors

Idea: Pluggable implementations

I hope this all makes perfect sense.