Methods & Return Values

Warmup

Below “casey” is an instance of the String class, #upcase is a method, and “CASEY” is the value that is returned.

"casey".upcase
#=> "CASEY"

• What is a method?
• What is a return value?
• What is an instance?
• How do you think the computer knows what to do when we call #upcase?

Methods

• Sets of instructions
• Allow us to DRY up our code
• Allow us to work at different layers of abstraction

Input/Output

• Methods take input and give us back some output based on the set of instructions they include.
• In this context:
  • Another word for inputis arguments
  • Another word for output is return value
• All methods return something (even if we don’t use it)
• Not all methods take input

Methods: Syntax

def method_name(arguments)
  # instructions
end

Methods: Syntax Example

def greeting(name)
  "Hello, #{name}!"
end

greeting("Sal")
#=> Hello, Sal!

Practice

Define two methods in IRB (signature and body) that will allow us to call them and get the results below:

body
#=> "Hope you're having a good day!"
signature("Sal")
#=> "Sincerely, Sal"

Multiple Arguments

• Methods can take more than one argument
• Arguments are separated by commas
• Arguments can be any kind of object (including Arrays, Hashes, etc.)

Methods in Methods

• You can call methods inside other methods
• This helps allow us to think of things at different layers of abstraction

def bake_cake(cake_recipe)
  instructions  = cake_recipe.instructions
  shopping_list = cake_recipe.ingredients
  ingredients   = purchase(shopping_list)
  bake(ingredients, instructions)
end

Practice

Create a method letter that uses the methods we’ve already defined that would produce the results below:

letter("Sal", "Ilana")
#=> "Hello, Sal! Hope you're having a good day! Sincerely, Ilana"

puts vs. Return

def greeting(name)
  "Hello, #{name}!"
end

greeting("Brian")

• Enter the code above in IRB. What happens?
• Enter the code above into a file called greeting.rb and run it with ruby greeting.rb. What happens?
• How can we make our greeting print out when we run our file?

Practice

Create a method print_letter that will print our letter to the terminal.

print_letter("Sal", "Ilana")
Hello, Sal! Hope you're having a good day! Sincerely, Ilana
#=> nil

• What do you notice is the difference between the return value of our letter and our print_letter methods?

Built In Methods

• Ruby has a lot of built-in methods that we can use without having to define them
• You are already familiar with many of them
• These can be found in the Ruby docs online and other resources

WrapUp

• How do we define methods in Ruby?
• What is the difference in how we define a method that takes arguments from one that does not?
• How do you call one method from within another method?
• Why do we use methods?