The document is a teaching material for a Ruby programming session, covering fundamental concepts such as objects, classes, duck typing, variables, strings, and methods. It explains these concepts with examples and emphasizes the importance of understanding how Ruby handles data and coding structures. Additionally, it provides reading assignments and exercises for further learning in the following weeks.

1. Learn Ruby 2011
Session 2

2. Our Sponsors
Flatsourcing, iSeatz, Koda, and Launchpad

3. Welcome Back
Ready to learn some Ruby?

4. Our Books

5. Learn to Program, 2ed
• For total beginners
• Systematic coverage of
programming concepts
• Uses Ruby to teach
programming

6. Programming Ruby, 3ed
• Comprehensive langauge
reference
• Covers Ruby 1.9.2,
annotations for 1.9 and
1.9.2 specific features
• de facto standard
reference

7. Language Crashing
Learning the basics in pieces

8. Objects vs Classes
• An Object is a discreet thing
• You can do things to Objects
• Classes tell you how to build Objects
• Classes in Ruby are also Objects

9. Objects vs Classes
• A Car is a Class
• My Car is an Object
• My Car has lots of things in common with
other cars
• So, My Car is a Car
• But, Not every Car is My Car

10. Everything is an Object
• In Ruby everything is an object
• This means you can do things to everything
you come across.

11. Everything has a Class
• Because everything is an Object, everything
also has a class
• An Object’s class is often referred to as it’s
Type

12. Duck Typing
• Ruby is Duck Typed
• This means that when you encounter an
Object in Ruby, what you can do to it
determines it’s type
• Ruby’s “Type Model” is concerned with
what you can do with Objects

13. A Sample of Ruby
def say_goodnight(name)
result = “Good night, “ + name
return result
end
puts say_goodnight(“John-Boy”)
puts say_goodnight(“Mary-Ellen”)

14. Variables
def say_goodnight(name)
result = “Good night, “ + name
return result
end
puts say_goodnight(“John-Boy”)
puts say_goodnight(“Mary-Ellen”)

15. Variables
• Variables hold values, in Ruby they hold
Objects
• Variables are the handles we use to easily
reference the data we want to work with

16. Variables
• There are four basic kinds of variables
• local_variables
• @instance_variables
• @@class_variables
• $global_variables

17. Variables
• There are also Constants, variables that
don’t change
• ClassNames
• CONSTANT_NAME

18. Variables
def say_goodnight(name)
result = “Good night, “ + name
return result
end
puts say_goodnight(“John-Boy”)
puts say_goodnight(“Mary-Ellen”)

19. Strings
def say_goodnight(name)
result = “Good night, “ + name
return result
end
puts say_goodnight(“John-Boy”)
puts say_goodnight(“Mary-Ellen”)

20. Strings
• Strings in Ruby come in two basic kinds
• “Double-Quoted”
• ‘Single-Quoted’
• They differ in how much processing Ruby
does with their contents

21. ‘Single-Quoted’ Strings
• Ruby does nothing with this kind of string,
no interpolation, no escape processing,
nothing

22. “Double-Quoted” Strings
• Ruby performs additional processing of
these strings
• Ruby looks for escape sequences
n t u2603
• Ruby also performs interpolation
#{expression}

23. Strings
def say_goodnight(name)
result = “Good night, #{name}“
return result
end
puts say_goodnight(“John-Boy”)
puts say_goodnight(“Mary-Ellen”)

24. Methods
def say_goodnight(name)
result = “Good night, #{name}“
return result
end
puts say_goodnight(“John-Boy”)
puts say_goodnight(“Mary-Ellen”)

25. Methods
• Methods are reusable bits of code
• They also go by the name Functions.
• They accept parameters, do something and
return a value

26. Methods
• Parameters are passed to methods and
given convenient local variable names by
the method definition

27. Methods
def say_goodnight(name)
result = “Good night, #{name}“
return result
end
puts say_goodnight(“John-Boy”)
puts say_goodnight(“Mary-Ellen”)

28. Methods
• When calling methods the parentheses that
surround parameters are optional.
• Only leave them out when unambiguous

29. Methods
def say_goodnight name
result = “Good night, #{name}“
return result
end
puts say_goodnight “John-Boy”
puts(say_goodnight “Mary-Ellen”)

30. Methods
• Methods return values can be either
explicit or implicit
• Use the return keyword to make explicit
what your methods return
• Or, the last expression in the method will
be the methods return value

31. Methods
def say_goodnight name
result = “Good night, #{name}“
end
puts say_goodnight “John-Boy”
puts(say_goodnight “Mary-Ellen”)

32. Our Simplified Sample
def say_goodnight(name)
“Good night, #{name}“
end
puts say_goodnight(“John-Boy”)
puts say_goodnight(“Mary-Ellen”)

33. Reviewing
• Objects vs. Classes
• Duck Typing
• Variables
• Strings
• Methods

34. For Next Week
For the New to Programming
• Read Chapters 2, 3 & 4 in LtP
• Complete exercises for each chapter
For Everyone
• Read Chapter 2 in PR1.9
• Keep playing in IRB

35. Next Week
• Arrays & Hashes
• Symbols
• Control Structures
• Regular Expressions
• Blocks & Iterators