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

"test".methods
2.methods

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.+(2)
1.send "+", 2

Array Iterators

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

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
end

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"}."
  end
end

@@@ 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]
end
@width, @height = dimensions

Metaprogramming

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
  end
end

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"

or-equals

def name
  @name ||= "Anonymous"
end

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

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