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Ruby Intermediate Introduction

This course goes deeper into Ruby. It builds on the beginner course, where you met blocks, modules and classes.

A beginner loop, revisited

An each loop walks a list one item at a time. Each item prints on its own line.

scores = [70, 85, 90]
scores.each do |score|
  puts score
end

A module mixed into a class

Greeter holds one greet method. Dog mixes Greeter in with include, so a dog object can call greet.

module Greeter
  def greet
    puts "Hello from the module"
  end
end
class Dog
  include Greeter
end
dog = Dog.new
dog.greet

A plain class at work

Box stores one label when it is built. The label method hands that label back.

class Box
  def initialize(label)
    @label = label
  end
  def label
    @label
  end
end
box = Box.new("tools")
puts box.label

Example

module Tagger
  def tag
    puts "Item: #{@name}"
  end
end
class Crate
  include Tagger
  def initialize(name)
    @name = name
  end
  def pack(items)
    items.each do |item|
      puts "Packing #{item}"
    end
  end
end
crate = Crate.new("Kitchen crate")
crate.tag
crate.pack(["cups", "plates"])

Key points

  • Blocks can take values and can be stored for later.
  • Modules mix shared methods into classes.
  • Classes follow fixed rules when they look a method up.
  • Files and errors get a fuller treatment in this course.
  • Every program here still runs as one file with ruby main.rb.

In this example, Crate mixes in the Tagger module and gains the tag method. The pack method takes a list and runs a block for each item. The tag line prints first, and then each packing line prints in list order.

Try it Yourself

Edit the code, then press Run.

Running is simulated

Exercise

What does include do inside a class?