rb-intro/README.md

Introduction

class You
  def ask_questions
    …
  end
end

class Me
  def keep_on_track
    …
  end
end

• Slide Time: 00:02 (00:02)
• Please ask questions at any time.
• Your job is to understand the material.
• My job is to keep us on track and on time.

30-second History of Ruby

Time.now + 30 * 60

• When and where?
• Influences.

• “Modern” Ruby.

• Slide Time: 00:02 (00:04)

• First released in 1995 by Japanese Programmer “Matz”.

• Syntax influenced by Perl (C-style).

• Features influenced by Smalltalk and Lisp.

• Modern Ruby began with v1.9 (2007)

• Several Implementations, main is MRI.

What is Ruby?

ruby.is_a?(Language)     &&
  ruby.typing?(:dynamic) &&
  ruby.memory?(:gc)      # => true

• Slide Time: 00:05 (00:09)
• Purely object-oriented.
• General purpose (not just web apps!)
• Dynamically typed.
• Garbage collected.

Ruby Syntax

class Person
  def initialize (first, last)
    @first_name = first
    @last_name  = last
  end

  def name
    @first_name + " " + @last_name
  end
end

character = Person.new("Sheldon", "Cooper")
character.name

• Slide Time: 00:08 (00:17)
• Perl-flavored, C-like syntax
• Semicolons are optional (line-based)
• Whitespace insignificant.
• Constants use CamelCase
• Variables and methods use snake_case.
• Blocks of code are delimited by begin...end or do...end.
• All methods return a value (no void functions).
• Implicit return of final value.
• The scope of a variable is determined by its name.

Everything is an Object

Consider this irb session:

>> 1.class
=> Fixnum
>> "Hello World".class
=> String

• Slide Time: 00:02 (00:19)
• Numeric literals are objects.
• String literals are objects.

Everything is an Object: Assignment

Open irb and experiment with the following:

• Numeric literals.
• String literals.
• true and false

• (0..10).class

• Slide Time: 00:06 (00:25)

Everything is an Expression

def create_logger
  logger = if $stdout.tty?
             Logger.new($stdout)
           else
             Logger.new("events.log")
           end
  …
end

• Slide Time: 00:02 (00:27)
• An if statement is really an expression.
• Using if in string interpolation.
• Class definition is an expression.
• Method definition is an expression.
• Loading a file is an expression.

Everything is an Expression: Assignment

Open irb and let’s play with some expressions together.

• Slide Time: 00:05 (00:32)
• if true then "hello" end
• if false then "hello" end

Object-oriented Programming

class Customer < Person
  include(UniqueID)
  private(:make_unique_id)
end

module UniqueID
  def make_unique_id
    …
  end
end

• Slide Time: 00:05 (00:37)
• Ruby only allows single inheritance.
• Multiple inheritance is emulated with modules.
• Modules are not interfaces.

Everything is an Object (Part 2)

Consider this irb session:

>> String.class
=> Class
>> anon = Class.new do
?>   def hello; "hi"; end
>> end
>> object = anon.new
>> object.hello
=> "hi"

• Slide Time: 00:05 (00:42)
• Even classes are objects!
• Creating classes at runtime.

Blocks and Iterators

list = ["Jasmine", "Lavender", "Lilac"]

# Long-form block.
list.each do |item|
  $stdout.puts("I like #{item}!")
end

• Slide Time: 00:03 (00:45)
• Blocks are borrowed from Smalltalk.
• Blocks can be used as iterators (Array#each).

Blocks and Iterators: Assignment

Open irb and play with long- and short-form blocks.

list = ["Jasmine", "Lavender", "Lilac"]

# Long-form block.
list.each do |item|
  $stdout.puts("I like #{item}!")
end

# Short-form block.
list.each {|item| puts(item)}

• Slide Notes: 00:08:00 (00:53:00)
• Long form: do |x| ... end.
• Short form: {|x| ... }.

Blocks and Resource Management

# Exception-safe file closing.
File.open("/dev/urandom") do |file|
  bytes = file.read(10)
  …
end

# Exception-safe database transactions.
transaction do
  record_a.save!
  record_b.save!
end

• Slide Notes: 00:04 (00:57)
• And also for resource management (File::open).
• You can write methods which accept blocks.
• Blocks can be passed around from method to method.

Closing

Open irb and ask some questions!

• Slide Time: 00:03 (01:00)