In our second session we began the first half of our language crash course. This session covered Classes vs. Objects, Duck Typing, Variables, Strings and Methods.

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