Intro to Ruby

Class 4

Welcome!

Homework Discussion

How was last week's homework? Do you have any questions or concepts that you'd like to discuss?

HW: English Numbers

You could expand the EnglishNumbers program by adding the following code to deal with thousands:

left  = number  # this line was original code, setting the 'left' variable

write = left/1000          #  How many thousands left to write out?
left  = left - write*1000  #  Subtract off those thousands.

if write > 0
thousands  = englishNumber write
numString = numString + thousands + ' thousand'

if left > 0
numString = numString + ' '
end
end

write = left/100 # this line begins the existing code that deals with hundreds
          

HW: Wedding Numbers

You could modify the code in the EnglishNumbers program to make it WeddingNumbers by replacing some of the added spaces with added 'and's and spaces:

# numString = numString + ' '   # old code

numString = numString + ' and '
          

HW: 99 Bottles of Beer

You could modify the code for 99 Bottles of Beer shown in Class2 to include the functionality in the EnglishNumber class:

require_relative 'englishnumber.rb'
num_bottles = 999

while num_bottles > 0
puts "#{englishNumber(num_bottles)} bottles of beer on the wall,
#{englishNumber(num_bottles)} bottles of beer, take one down, pass it
around, #{englishNumber(num_bottles - 1)} bottles of beer on the wall!"

num_bottles = num_bottles - 1
end
          

Review

• What is a method?
• Creating & calling a method
• What is an object?

What would you like to see reviewed?

Built in classes of Ruby

Ruby has many classes predefined:

• String
• Integer
• Float
• Array
• Hash

They are commonly used object types, and have methods associated with them already. How convenient!

a = Array.new
b = String.new
          

Built in classes of Ruby

When we create new objects from these classes, we can do things with them immediately.

To see all methods associated with an object or class, run ".methods" on it.

b = "holy cow!"
b.methods
          

You can view all the built in classes and their associated methods in the Ruby documentation.

Extending a Class

You can write new methods for the built in classes of Ruby. They will then be available to all instances of that class in your program.

class String
def get_excited
wow = self + "!!!"
return wow
end
end
          

"self" refers to the object calling the method.

You can redefine existing methods for classes this way, too, but it's not recommended.

Creating a Class

It's very easy to create your own classes in Ruby.

# die.rb
class Die

def roll
@numberShowing = 1 + rand(6)
#rand(6) returns a random-ish number between 0-5
end

def showing
return @numberShowing
end

end
          

Inside the class, define its methods.

Creating a Class

You can use your class right away by loading it into IRB.

#in irb
load 'die.rb'
die = Die.new
die.roll
puts die.showing
        

You can use it in another file by requiring it. We'll discuss this later.

Refactoring a Class

What is the result of calling the .showing method on a newly-created, un-rolled Die object?

We can avoid this by calling the roll method as part of the creation of a new instance of Die.

# die.rb
class Die

def initialize
roll
end

def roll
@numberShowing = 1 + rand(6)
end

def showing
@numberShowing
end

end
          

Let's Develop It

• In your text editor, create your own class with an initialize method, and at least one other method.
• Open IRB and load the class. Create one or more objects from the class and run some methods on them.
• You could use the next slides as an example.

Example of creating a class

# in character.rb
class Character

def initialize(name)
@name = name
@health = 10
end

def heal
@health += 6
end

def adventure
if @health > 0
puts "#{@name} goes on a great adventure and meets a dragon!"
puts "The dragon hugged #{@name} kind of hard..."
@health -= 5
else
puts "#{@name} is dead :("
exit
end
end

end
          

Running example program in IRB

# in irb
load 'character.rb'
me = Character.new("Cheri")
me.adventure
me.heal
me.adventure
# repeat until you're done having fun

          

Inheritance

Classes can inherit from one other class.

All elves are characters, so if all characters have an adventure method, so do all elves. Elves may also have their own methods that other characters do not.

Inheritance

Denote that Elf inherits from Character by using the < symbol

# in character.rb, after Character class code
class Elf < Character
def twinkle
puts "I'm super magical!"
end
end

#in irb
load 'character.rb'
me = Elf.new("Cheri")
me.adventure
me.twinkle
          

Notice that the initialize method was also inherited, as our new Elf knows its name and started off with 10 health.

Inheritance

Subclasses may differ from from their super classes in some ways. Methods can be overwritten when this is the case.

# in character.rb, after Character class code
class Elf < Character
def twinkle
puts "I'm super magical!"
end

def heal
@health += 8 # it's easier to heal when you're magic
end
end

#in irb
load 'character.rb'
me = Elf.new("Cheri")
me.heal
          

More information about inheritance can be found here.

Putting it all together

For a command line program, you need these pieces:

1. File(s) containing your class definitions
2. A file containing your program, which requires the class file(s)
3. To call the program file from the command line (not IRB)

Putting it all together

The file containing your class definitions, here called character.rb:

# in character.rb
class Character
# contents of class here
end

class Elf < Character
# contents of class here
end
            

Putting it all together

The file containing your program, here called adventure.rb, which requires the class file:

# in adventure.rb
require_relative 'character.rb'
#file path relative to the location of adventure.rb file
require_relative 'die.rb'


puts "Your name?"
char = Character.new(gets.chomp)
# plus lots more adventuring.....
            

Putting it all together

Call the program file from the command line:

#in command line
ruby adventure.rb
# then have some fun!
            

Let's Develop It

Putting it all together: A role-playing game!

• If you didn't write a Character class, copy and paste the code to get one started.
• Create a few subclasses of Character.
• Write a command-line program that calls your character and die classes to allow the user to have an adventure!
• Maybe user can choose their character type?
• Maybe the user's progress will be dependent on outcome of dice-rolling?

Questions?

Further Resources

Homework

Practice: Make your final project even bigger and better! If you're taking this class as part of a job plan, attend a local meetup and talk to a couple of strangers about what you've learned and what you're excited about doing with programming.