Tuples

Mix.install([
  {:jason, "~> 1.4"},
  {:kino, "~> 0.9", override: true},
  {:youtube, github: "brooklinjazz/youtube"},
  {:hidden_cell, github: "brooklinjazz/hidden_cell"}
])

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Review Questions

Upon completing this lesson, a student should be able to answer the following questions.

• What is a tuple and how do you create one?
• How do you pattern match on a tuple to bind elements in the tuple to variables?

Tuples

Tuples are fixed size containers for multiple elements. Like lists they can contain any data type.

{}
{7}
{1, 2, 3}
{"example"}
{1, "pizza", 3, :success, false}

They are often used when you know the number of desired elements and their type. For example, it’s common in Elixir to use tuples to represent failure or success cases with the associated error message or success value.

{:success, "Well done!"}
{:error, "Too bad!"}

Your Turn

In the Elixir cell below, create a tuple with :ok as the first element, and "got it!" as the second element.

Example solution

{:ok, "got it!"}

result = "got it!"
{:ok, result}

Pattern Matching

In Elixir, the = sign is the match operator. In other programming languages, you may call it the assignment operator.

Elixir calls = the match operator because it uses pattern matching to bind variables.

What is pattern matching? Well rather than simply assigning values to variables, Elixir allows you to bind variables on the left-hand side of the =. So long as it matches the same shape of the right hand side of the =.

For example, the following expression is the most “strict” match possible. Both sides are exactly equal.

{1, 2, 3} = {1, 2, 3}

The = operator attempts to coerce the left side value to match the right side value, so when we write the following expression, we bind my_tuple to {1, 2, 3} in order to make the right and the left side match.

The coercion to match is less obvious with a simple variable name, because it’s like a blank canvas, it can match any value.

my_tuple = {1, 2, 3}

However, we can bind other values inside of a container data type, so the left and right side still match.

{one, two, three} = {1, 2, 3}

Now we can use these bound variables one, two, and three in our program.

one

two

three

So long as the expression on the left side of match operator = matches the pattern of the right side, you can bind variables to values.

The tuple with variables bound on the left side must have the same number of elements as the tuple on the right side, otherwise we’ll cause a MatchError.

{one, two} = {1, 2, 3}

If we want to bind some of the variables in a tuple, and ignore others, we can use an _ to ignore any variables.

{one, _two, three} = {1, 2, 3}

You can pattern match with any kind of data. So long as the left side matches the right side. We’ll cover pattern matching with other data structures in later reading material.

Your Turn

Use pattern matching to bind "jewel" to a variable called jewel. Replace jewel with your answer.

Example solution

{_gold, _treasure, jewel} = {"gold", "treasure", "jewel"}
jewel

{_, _, jewel} = {"gold", "treasure", "jewel"}
jewel

Further Reading

Consider the following resource(s) to deepen your understanding of the topic.

• Elixir Lang: Tuples
• Exercism: Tuples
• Elixir Schools: Tuples
• HexDocs: Tuple

Commit Your Progress

DockYard Academy now recommends you use the latest Release rather than forking or cloning our repository.

Run git status to ensure there are no undesirable changes. Then run the following in your command line from the curriculum folder to commit your progress.

$ git add .
$ git commit -m "finish Tuples reading"
$ git push

We’re proud to offer our open-source curriculum free of charge for anyone to learn from at their own pace.

We also offer a paid course where you can learn from an instructor alongside a cohort of your peers. We will accept applications for the June-August 2023 cohort soon.

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