More Neat Things About Ruby

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.

Reopening classes

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

4.divisible_by? 2 #=> true
4.divisible_by? 3 #=> false

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;
    • we care what it does

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

@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.

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

Operators are Methods


1 + 2
1.send "+", 2

send the object 1 the message + with the parameter 2

Operator Overriding

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