Hi, I'm Nicholas Johnson!

software engineer / trainer / AI enthusiast


Functions are declared using the def keyword:

def greeting
  puts "Hello Ruby"

  => Hello Ruby

Accepting parameters

Functions can accept parameters as you would expect. We pass them like this:

def greet(name)
  puts "hello #\{name}"

  => "hello dave"

Optional braces

When calling a function, the braces are optional.

greet "dave"
  => "hello dave"

This is a really nice syntax, and comes into it’s own when we start writing methods.

Returning a Value

Functions can return a value. We pass back a value using the return statement, like so:

def say_hello_to(name)
  return "hello #\{name}"

puts say_hello_to "dave"
  => "hello dave"

get_greeting_for “dave” evaluates to the string “hello dave”. This string is received by puts, which then outputs it to the screen.

Optional return statements

The return statement is also optional. If it’s omitted the function will return the last evaluated expression, so:

def get_greeting_for(name)
  "hello #\{name}"

puts get_greeting_for "dave"
  => "hello dave"

This is a clean and useful syntax for short methods such as getters.

Default Values

We can set the default value of an argument, so if no value is passed, our function will still work:

def get_greeting_for(name="anonymous")
  return "hello #\{name}"

puts get_greeting_for
  => "hello anonymous"

Note that if we have several arguments, and some are missing, they will be filled in from left to right, so the last ones will take their default values.


  • Functions in Ruby are created using the def keyword (short for define).
  • Functions that exist in an object are typically called methods.
  • Functions and methods are the same, except one belongs to an object.
  • Objects are created from classes using the .new method

Exercise - Meet and greet

Write a simple function that greets a person by name. It should receive a name and return a string.

If it is called without parameters it should say “Hello anonymous”

Exercise - A simple function

Write a function which receives a value and outputs a string containing all the numbers up to and including that value.

Integrate this into a command line app.