Strings

Mix.install([
  {:jason, "~> 1.4"},
  {:kino, "~> 0.8.0", override: true},
  {:youtube, github: "brooklinjazz/youtube"},
  {:hidden_cell, github: "brooklinjazz/hidden_cell"}
])

Navigation

Return Home Report An Issue

Setup

Ensure you type the ea keyboard shortcut to evaluate all Elixir cells before starting. Alternatively you can evaluate the Elixir cells as you read.

Review Questions

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

• What are strings, and what kind of information are they useful for storing?
• How do we add two strings together using string concatenation?
• How do we interpret Elixir code inside of a string using string interpolation?

Strings

A string is any sequence of characters contained within two double quotes "". A character is any single number, letter, or symbol.

"T" # letters
"t" # letters
"1" # numbers
"1.2" # numbers
"&" # symbols
"_" # symbols

You can visualize a string as characters joined together by strings. Strings can be a single character, no characters, or many characters!

flowchart LR
  S --- T --- R --- I --- N --- G

Strings can contain single quotes and other symbols such as !@#$%^&*()_+-=';: and more.

"!@#$%^&*()_+-=';:"

They are useful for representing all kinds of information as text.

Your Turn

In the Elixir cell below, create a string "Hello, world!". This is a rite of passage for every programmer.

Multiline Strings

Sometimes we want to represent a string with multiple lines. The newline \n character represents a new line in a string.

string = "line 1\nline 2\nline 3"

IO.puts(string)

To make defining multiline strings easier, Elixir allows us to use three quotes """ to define a multiline string.

string = """
line 1
line 1
line 1
"""

IO.puts(string)

String Operators

String operators allow us to manipulate strings.

The <> operator joins two strings together. Joining strings together is called string concatenation.

"hello, " <> "world."

Only strings can be concatenated together using the <> operator. You’ll notice concatenating 1 causes an error expected binary argument in <> operator but got 1 This error occurs because we’re asking the computer to concatenate a string with an integer.

"hello" <> 1

Your Turn

In the Elixir cell below, use string concatenation to join "Hi " and the name of one of your classmates.

So "Peter" would be come "Hi Peter.".

Replace nil with your answer.

Example solution

"Hi " <> "Peter."

String Interpolation

Using #{}, We can also interpolate values in strings. Essentially, this means we can evaluate code inside of a string. The code you want to interpolate inside of the string goes between the curly braces {}.

So we can evaluate 4 + 4, which equals 8 inside a string.

"I have #{4 + 4} apples."

String interpolation is often useful when your string has many computed values or tricky punctuation. Otherwise, it’s easy to make mistakes.

Notice that there’s a grammar mistake below that could easily be missed when using string concatenation.

"I have" <> "8" <> "apples"

Your Turn

In the Elixir cell below, use string interpolation to say I have #{X - 1} classmates.. Where X is the number of people in your cohort including yourself.

Example solution

"I have #{1 - 1} classmates."

answer = nil

Escaping Characters

Elixir allows you to use Escape Characters to represent special values in a string. We’ve already seen the \n escape character for a newline.

For example, we can use the \ symbol to escape special characters in a string. This is handy when you want to include characters that would have alternative meaning in the string. For example, if you wanted to include double quotes in a string, you can escape the double quote \".

string = "They said \"so this is how you include double quotes in a string!\""

IO.puts(string)

There are other special characters such as backslashes \, or interpolation syntax that you might want to escape.

string = "Use \#\{\} to interpolate a value in a string"

IO.puts(string)

string = "If you don't escape using backslash \\, then #{} doesn't appear"

IO.puts(string)

Further Reading

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

• Joy of Elixir: Strings
• Elixir-lang: binaries, strings, and charlists

Mark As Completed

file_name = Path.basename(Regex.replace(~r/#.+/, __ENV__.file, ""), ".livemd")

save_name =
  case Path.basename(__DIR__) do
    "reading" -> "strings_reading"
    "exercises" -> "strings_exercise"
  end

progress_path = __DIR__ <> "/../progress.json"
existing_progress = File.read!(progress_path) |> Jason.decode!()

default = Map.get(existing_progress, save_name, false)

form =
  Kino.Control.form(
    [
      completed: input = Kino.Input.checkbox("Mark As Completed", default: default)
    ],
    report_changes: true
  )

Task.async(fn ->
  for %{data: %{completed: completed}} <- Kino.Control.stream(form) do
    File.write!(
      progress_path,
      Jason.encode!(Map.put(existing_progress, save_name, completed), pretty: true)
    )
  end
end)

form

Commit Your Progress

Run the following in your command line from the curriculum folder to track and save your progress in a Git commit. Ensure that you do not already have undesired or unrelated changes by running git status or by checking the source control tab in Visual Studio Code.

$ git checkout -b strings-reading
$ git add .
$ git commit -m "finish strings reading"
$ git push origin strings-reading

Create a pull request from your strings-reading branch to your solutions branch. Please do not create a pull request to the DockYard Academy repository as this will spam our PR tracker.

DockYard Academy Students Only:

Notify your teacher by including @BrooklinJazz in your PR description to get feedback. You (or your teacher) may merge your PR into your solutions branch after review.

If you are interested in joining the next academy cohort, sign up here to receive more news when it is available.

Up Next