Ruby Tutorial: More Neat Things

More Neat Things About Ruby

(If You Think Programming Languages Are Neat)

This section is a continuation of "ruby intro", covering more advanced topics. It is still intended as a brief, lightweight overview of the Ruby language; following sections will cover all these topics in much more detail.

Everything is an object

@@@ ruby
"test".upcase   #=> "TEST"
"test".class    #=> String


1.to_s       #=> "1"
"1".to_i     #=> 1
:hello.class #=> Symbol

Methods are messages

@@@ ruby
thing.munge(4, 10)
thing.munge 4, 10
thing.send "munge", 4, 10

All of the above send the object "thing" the message "munge" with the parameters 4 and 10.

Operators are Methods

@@@ ruby
1 + 2
1.send "+", 2

Array Iterators

@@@ ruby
my_array = ["cat", "dog", "world"]
my_array.each do |item|
  puts "hello " + item

Hash Iterators

@@@ ruby
my_hash = { :type => "cat",
            :name => "Beckett",
            :breed => "alley cat" }
my_hash.each do |key, value|
  puts "My " + key.to_s + " is " + value

The Default Block

  • Methods can take block arguments
  • Use either do...end or {...} at the very end of the argument list
  • Inside the method, call the default block with yield

Iterators use the Default Block

@@@ ruby
fruits = ["apple, "banana", "cherry", "date"]
my_array.each do |item|        #<< start of default block
  puts "Yum! I love #{item}!"
end                            #<< end of default block   

Blocks are like mini-functions

  • Blocks can also take parameters or return a value
  • e.g. the map iterator translates each item in an array into a new array

      @@@ ruby
      >> ["hello", "world"].map {|string| string.upcase}
      => ["HELLO", "WORLD"]
  • {|string| string.upcase} defines a block

duck typing

  • If it looks like a duck...
  • and it quacks like a duck...
  • then it is a duck!
  • In other words, we don't care what an object is as long as it does what we want

duck typing example

@@@ ruby
def print_even_or_odd(collection)
  collection.each do |item|
    puts "#{item} is #{item.even? ? "even" : "odd"}."
@@@ ruby
print_even_or_odd [1, 2, 3]
print_even_or_odd 1..3

Modules and Mixins

  • Any class (or object) can include a Module
    • also known as mixing in
    • so Modules are also called mixins
  • Modules provide behavior but no state
    • more precisely, they affect the extending object's state
  • Provides most of the power of multiple inheritance, but less confusing

Array Assignment

@@@ ruby
@width, @height = width, height
@width, @height = [width, height]

def dimensions
  [10, 20]
@width, @height = dimensions


  • macros (class methods)
    • attr_accessor
    • has_many

Classes are objects

  • class methods are really just methods on the class object
  • code evaluated in the scope of a class definition acts on the class object

Domain-Specific Languages (DSLs)

  • Rails
  • Rake
  • Cucumber
  • Rspec
  • etc.

the method_missing method

What do you do when you don't know what to do?

private vs public

  • Private really just means "please don't come in."
  • If someone has access to your runtime environment, they are trusted.
  • Spend your time writing code (and testing it), not protecting yourself from other code

Reopening classes

@@@ ruby
class Fixnum
  def divisible_by? n
    self % n == 0

4.divisible_by? 3 #=> false

No Function Overloading

  • Some OO languages allow several methods with the same name but different parameters...
  • ...but not Ruby!
  • If you redefine a method, the new one replaces the old one
  • There are tricks to save the old method if you need to call it
    • alias, alias_method, alias_method_chain

Operator Overriding

  • operators like +, *, <<, etc. are defined as methods
  • so they can be overridden
  • String has some great ones
      "abc" * 3           #=> "abcabcabc"
      "abc" << "def"      #=> "abcdef"
      "%d live crew" % 2  #=> "2 live crew"


def name
  @name ||= "Anonymous"
  • Means "if @name has a value, use it, but otherwise make it 'Anonymous'"
  • Relies on "logical or" and "nil is false" semantics
  • There's also "plus-equals" (+=) and so forth