Ruby Functions & Methods: How to Define Your Own

What is a Ruby method?

A method is a set of one or more lines of Ruby code that are grouped together for a specific purpose.

The grouped code is given a name for easy reuse without the need for rewriting or copying & pasting the code.

The purpose of a method can be to:

  • GET information.
  • CHANGE or CREATE objects.
  • FILTER & FORMAT data.

Example 1:

The size method on an Array object gives you a count of elements (get information).

Example 2:

The pop method removes the last element from the array (change objects).

When you understand the relationship between objects, classes & methods everything starts to make sense.

Relationship between Ruby objects, classes and methods.

Let’s keep learning!

How to Define Methods

The Ruby programming language has many powerful built-in methods you can use, but you can also create your own.


You can define your own instance method using the def keyword.

Here’s the syntax:

def gimme_bacon
  puts "Bacon plz."

What’s going on here?

  1. def is part of Ruby’s syntax, it says that we want to define a method
  2. gimme_bacon is the name of the method
  3. puts "Bacon plz." is the body of the method
  4. end marks the end of the method definition

Defining a method only tells Ruby that you want to create it.

If you want to use it then you need to call the method.

How to Call Methods in Ruby

In Ruby, when we use a method, we say that we’re calling it.

You’ll often hear “method call”, or if you’re working with someone who’s an Object-Oriented purist, you may hear that “you’re sending a message”.

Either way…

Let’s see an example of using a method.

Here you go:


This prints:

"Bacon plz."

You can call methods on objects.

For example:

n = [1,2,3]

# 3

This n.size is calling the method size on the object n, which happens to be an Array.

The result?

We get the array’s size.

What methods are available?

That depends on the class of the object you’re calling the method on.

An array is going to have different methods than a hash.

You can check the Ruby documentation to find a list of methods for a given class.

How to Return Values (Basic Syntax)

One key concept in Ruby is that ALL methods return a value.

Let me explain!

As a result of calling a method, you get something back.

This “something” that you get comes from the last expression in your method definition.

Here’s what I mean:

def number_one

# 1

Another example:

def add(x,y)
  x + y

add(5, 6)
# 11

We call this an “implicit return”, just a fancy name for “automatically return the last thing”.

In addition:

You can tell Ruby to return something with a keyword.

def two
  return 2

# 2

Notice that unlike other languages this return statement is NOT required & your method will stop running as soon as it finds return.

You can use this is for an early return (guard statements are good example), or to exit a loop.

Why is There a Question Mark in My Method Name?

You may find some strange Ruby methods.

With names like:

  • empty?
  • sort!
  • title=

ALL of these are valid method names.

What does the question mark, the exclamation mark, or the equals sign mean?

They are conventions in the Ruby community.


  • A question mark method, also known as a predicate method, is supposed to return either true or false
  • An exclamation mark method says that it will do something different than the non-exclamation mark version. Usually, this is associated with changing the object itself in some way, like adding / deleting elements. Also known as “bang methods”.
  • The equals sign method means assignment. It’s used to assign a value to an instance variable.

None of these conventions are enforced by the language.


If you follow them, you’ll be able to write more Ruby-like code!


You’ve learned about the power of Ruby functions, how to define them, use them & how to follow proper conventions.

Now it’s your turn to put this into practice 🙂

Thanks for reading!

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