Intro to Programming with Ruby
Class 3
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Homework Discussion
How was last week's homework?
Do you have any questions or concepts that you'd like to discuss?
Is anyone BRAVE enough to show what they have?
The Homework was:
- Ranges problem
- Pet shop
- Bye Grandma
HW: grandma.rb
chatting = true
byes = 0
while chatting
puts "Ask Grandma a question:"
said = gets.chomp!
if said == "BYE"
byes += 1
if byes > 2
chatting = false
else
puts "** Grandma is ignoring you **"
end
elsif said == said.upcase
year = 1930 + Random.rand(20)
puts "NO, NOT SINCE #{year}!"
else
puts "HUH?! SPEAK UP, SONNY!"
end
end
puts "Thanks for chatting with Grandma"
Review
- Conditions -
if,elsif,else - Loops -
while,for - Arrays -
[1,2,3] - Ranges -
[1..3] - Hashes -
{"one" => 1, "two" => 2}
What we will cover today
- Methods / Functions
- Objects
- Object Oriented Programming
Methods
A method is a name for a chunk of code
Methods are often used to define reusable behavior.
Let's look at a method we've already used:
If you have code you want to reuse or organize, methods will help.
Method VS Function
Question: "Are methods and functions the same thing?"
Answer: "For the most part"
Functions are chunks of code you can re-use
Methods are Functions that exist on objects
Doesn't make sense? Don't worry! It's not really that important right now!
For the purpose of this class, call them whichever word you want
Writing A Method
Just like with loops and conditionals there is a term used to declare a method, def and end
def means define
subtract is the name of the method
x, y are parameters
x - y is the body of the method
x - y is also the return value
Calling A Method
Arguments are passed
and parameters are declared.
Note that the variable names don't have to match!
In this code, 5 is an argument and x is a parameter
Class: Write this code into irb and call out what the results are!
def subtract(x,y) #parameters
x - y
end
subtract(5, 2) #arguments
Returning Values
Every Ruby method returns something.
Usually, it's the last statement in the method.
It could be the value sent to return if that came first.
Class: Write this code into irb and call out what the results are!
def subtract_a(x,y)
x - y
'another thing'
end
return_value = subtract_a(5, 2)
puts return_value
def subtract_b(x,y)
return x - y
'another thing'
end
return_value = subtract_b(5, 2)
puts return_value
Local Variables
A local variable is a variable whose scope ends (goes out of context) when the function returns
Class: Write this code into irb and call out what the results are!
Splat Arguments
Only in 1.9 or newer
The Splat or asterisk operator will capture however many arguments you pass into greet.
If you might want to pass in a different number of arguments each time, a Splat argument might be the right choice!
def greet(greeting, *names)
names.each do |name|
puts "#{greeting}, #{name}!"
end
end
>> greet("Hello", "Alice", "Bob", "Charlie")
Hello, Alice!
Hello, Bob!
Hello, Charlie!
For more explaination check out this link
Default Values
If using 1.9 or lower, these have to be the last arguments in your list.
Default values are used if the caller doesn't pass them explicitly.
def eat(food = "chicken")
puts "Yum, #{food}!"
end
>> eat
Yum, chicken!
>> eat "arugula"
Yum, arugula!
Hashes as Parameter
def add_to_x_and_y(amount, vals)
x = vals[:x]
y = vals[:y]
x + y + amount
end
add_to_x_and_y(2, {:x => 1, :y => 2})
Let's Develop It!
Lets write a method called calculator. It will take 2 numbers, like 22 and 5, and a string like "divide". For now, just do "add", "subtract", "multiply", and "divide"
Cheat!
Here is some help to get started
def calculate(first_num, second_num, operation)
# Do something different based on operation!
end
Objects and Classes
"A Class is to an Object like a Book is to Mary Shelley's Frankenstein"
Classes
Everything has a Class.
Classes define a template for objects. They describe what a certain type of object can do and what properties it has.
There are many kinds of classes you've already been using, including:
String, Number, Array, Hash, Time, ...
Objects
An Object is an instance of a Class
Objects do things and have properties.
To create an instance of a class (aka: Object) we use .new
arr now refers to an instance of the class Array
Object: Number
What can it do?
- Add +
- Subtract -
- Divide /
- Multiply *
Sample properties?
- len - What is the length?
- base - What base is the number in? (2, 10, 16?)
- even - Is the number even, or odd?
Object Methods
Methods can be defined on objects.
Class: Write this code into irb and call out what the results are!
class MyObject
def delete
puts "Deleted the thing!"
end
end
o = MyObject.new
puts o.methods.include?(:delete)
Instance Variables
Represent object state
Names start with an @
Only live inside the object
Class: Write this code into irb and call out what the results are!
class Cookie
def add_chips(num_chips)
@chips = num_chips
end
def yummy?
@chips > 100
end
end
cookie = Cookie.new
cookie.add_chips(500)
puts cookie.yummy?
Object Oriented Programming
- Object Oriented Programming is one of many paradigms of programming: procedural, event-driven, functional, declarative...
- It's very common to encounter OOP in most companies, and especially in certain languages: Java, Ruby, C#, Python
- ... But! Some languages are good at more than one paradigm! (We're going to focus on OOP, though)
- All this means is that programs are organized around objects (data & methods).
- You might choose OOP because Objects make things easier to understand and act as a natural way to modularize code.
OOP & Encapsulation
One thing that makes code easier to maintain is Encapsulation which is one of the fundamentals of OOP.
Encapsulation is a nice way of saying "put all my properties/behaviors in my capsule where other objects can't touch them".
By assigning certain responsibilities to objects, code is more purposeful and less likely to be changed by accident.
Real World Example: You don't need to know how the engine works to drive your car - you just need to know Start, Accelerate, Slow, and Off
OOP & DRY
DRY stands for Don't Repeat Yourself
Code is said to be DRY when you don't have any copy/pasted code in multiple places - when each line that can be re-used, is.
DRY goes well beyond just OOP, but OOP makes DRY code easy, since everything lives in a class or object that you can re-use!
Think about how you can use Encapsulation to make your code more DRY
OOP & Inheritance
Just as you inherited traits from your parents, your classes may inherit traits from other classes.
Inheritance is when you use one class as the basis for another.
You might use Inheritance if two classes have the same properties and methods, but one will add some additional functionality the other doesn't need.
This way you don't need to write the same thing twice.
class MyString < String
end
my_string = MyString.new
my_string.upcase
OOP & Polymorphism
- Similar to inherited traits and behaviors, there are also polymorphic traits and behaviors.
- Polymorphic means many forms.
Within OOP, this relates to different objects being able to respond to the same message in different ways.
Questions?
Homework
Expand upon the calculate method from class.
Make a class called "Calculator", and make each operation ("add", "subtract", "multiply","divide") into a method on Calculator
Run a demonstration of having all of the operations return a correct result!
Intro to Programming in Ruby
@gdiboston
We are done with class 3!
We have done a lot, I know you have questions so ask them!