Ruby: What extend and include do

All Rubyists should be familiar with the common definitions for include and extend. You include a module to add instance methods to a class and extend to add class methods. Unfortunately, this common definition isn’t entirely accurate. It fails to explain why we use instance.extend(Module) to add methods to an instance. Shouldn’t it be instance.include(Module)? To figure this out we’re going to start by discussing where methods are stored.

include: Adds methods from the provided Module to the object
extend: Calls include on the singleton class of the object

Ruby blocks: Braces and do/end have different precedence

TL;DR {} binds stronger than do … end (as always in Ruby, special characters bind stronger than words)

Demo

Right way

names = ['bRUce', 'STaN', 'JOlIE']

# Blocks in braces are passed to the rightmost method
print names.m...

Posted by Dominik Schöler to makandra dev (2013-04-10 07:01)

Ruby: What extend and include do

Further reading

Related cards:

||= and &&=

Introduction

Demo

Right way

`||=` and `&&=`