A brief and simple introduction to classes in Ruby.

1. Basic Object
Oriented Programming
With Ruby!

2. Everything's An Object!
"Hello, World!" # A String Object
["one", "two"] # An Array Object
# A Hash Object (with Symbol Object keys and String values!):
{
username: "johndoe",
password: "guessme"
}
1 # An Integer Object
3.23421 # A Float Object

3. Objects Have State

4. Objects Have State
State is basically data: the value or values that
represent the aspects of the object.
"Hello, World"
# This object has only one piece of state,
# a string of characters spelling "Hello World"

5. Objects Have State
What is the state in a String object?
# A String is an Array of characters
"Hello".chars # => ['H', 'e', 'l', 'l', 'o']

6. Objects Have Methods

7. Objects Have Methods
Methods operate on state:
4 To change the state
4 To return a changed copy of the state.

8. Objects Have Methods
"Hello, World!".downcase # => "hello, world!"
["one", "two"].reverse # => ["two", "one"]
hash = {
username: "johndoe",
password: "guessme"
}
hash.delete(:username) # => "johndoe"
hash # => {:password=>"guessme"}
1.to_f # => 1.0
3.23421.to_i # => 3

9. You Can Make Objects Too!

10. How To Write An Object
4 "Class": another name for Object
4 Objects are defined in files

11. How To Write An Object
# File Name: better_string.rb
class BetterString
end
Now we can make a BetterString:
better_string = BetterString.new

12. How To Write An Object
class BetterString
def initialize(base)
end
end
Now we can do:
better_string = BetterString.new("A boring string")
# Oh noes, our base string isn't saved!
better_string.inspect # => "#<BetterString:0x007f8d7c1e6c78>"

13. How To Write An Object
class BetterString
def initialize(base)
# This creates a LOCAL variable, only this method can see it
base = base
# This creates a INSTANCE variable (state)
@base = base
end
end
When you want to save state, use an instance variable.

14. How To Write An Object
class BetterString
def initialize(base)
@base = base
end
end
better_string = BetterString.new("A boring string")
better_string.inspect
# => "#<BetterString:0x007fa633091998 @base="A boring string">"
better_string.base
# ~> -:11:in `<main>': undefined method `base' for #<BetterString ...> (NoMethodError)
# What gives?

15. Getters and Setters

16. Getters and Setters
class BetterString
def initialize(base)
@base = base
end
# A getter for the @base variable
def base
@base
end
# A setter for the @base variable
def base=(new_base)
@base = new_base
end
end

17. Getters and Setters
better_string = BetterString.new("A boring string")
better_string.base # => "A boring string"
better_string.base = "An awesome string" # => calls the base= setter
better_string.base # => "An awesome string"

18. Shortcuts!

19. attr_reader, attr_writer
class BetterString
attr_reader :base # getter
attr_writer :base # setter
def initialize(base)
@base = base
end
end

20. attr_accessor
The shortcut to rule them all

21. attr_accessor
class BetterString
attr_accessor :base # both getter and setter!
def initialize(base)
@base = base
end
end

22. Review

23. Review
4 Objects are a combination of state and methods
4 You define classes in files
4 Use @instance methods to save state
4 Use attr_accessible, attr_writer, attr_reader to
make getters and setters

24. So...
Can we make BetterString
DO SOMETHING?

25. Make Strings Awesome-er
class BetterString
# ...
def improve
@base.gsub("boring", "awesome")
end
end
better_string = BetterString.new("A boring string")
better_string.improve # => "A awesome string"

26. Class / Instance Methods

27. Class / Instance Methods
Class: The Platonic definition of the object.
Instance: A version of that object, assigned to a
variable.

28. Class / Instance Methods
BetterString # This is the class
better_string = BetterString.new # This is an instance
# Class methods can be called on the class
BetterString.from_str("Some other string")
# Instance methods can be called on instances
better_string.improve

29. Class / Instance Methods
class BetterString
# This is a class method
def self.from_str(other_string)
BetterString.new(other_string)
end
# This is an instance method
def improve
# ...
end
end

30. Equality

31. Equality
normal_string = "A boring string"
better_string = BetterString.new("A boring string")
normal_string == better_string # => false
# Whaa??

32. Equality
We can "overload" the == operator for BetterString.
class BetterString
# ...
def ==(other_string)
@base == other_string
end
end
normal_string = "A boring string"
better_string = BetterString.new("A boring string")
normal_string == better_string # => true
# Yay!

33. First Equality
Then the World!

34. Operator Overloading
We can override all kinds of operators for objects.
4 Addition
4 Subtraction
4 Multiplication
4 Division
4 Equality

35. Review

36. Review
4 Ruby is completely object-oriented
4 Objects are a combination of state and methods
4 Even operators are just methods!

37. A Note About Rails...
Everything in Rails is a plain old Ruby Object.
(PORO for short)
Controllers, Models, Tests, they're all classes.

38. Go Forth and Conquer.