Elixir Cheatsheet

I’ve been trying to play around with Elixir, I’ve decided to make a little cheatsheet to remember the basics.

Source for documentation: HexaDocs.

Operators

Match Operater

In Elixir there is not concept of “assignment”, the = operator is a match operator, not an assignment operator.

iex(1)> hello = :hello
hello
iex(2)> {status, msg} = {:error, "You've dropped the ball!"}
{:error, "You've dropped the ball!"}
iex(3)> status
:error

Equal Operator

Check if two things are equal ==:

iex(1)> true == :true  # See booleans - true is attached to the atom :true
true
iex(2)> 2 + 2 == 4
true

The Pipe Operator

Takes pipe operator |> the output of a function and uses it as the first argument in the next function.

iex(1)> add_3 = fn a -> a + 3 end
#Function<42.105768164/1 in :erl_eval.expr/6>
iex(2)> iex(4)> [1, 3, 5] |>
...(2)> Enum.sum |>
...(2)> add_3.()    # Equivalent to: add_3.(Enum.sum([1, 3, 5]))
12

Basic Data Types

For more documentation, see the HexaDocs.

Booleans

Whether something is true of false. (Attached from atoms :true or :false).

Atoms

Atom are constants. Their name is their value - and they are used similarly to enums in other languages. One of the most common atoms used in elixir is :ok.

Example use of atoms:

tup1 = {:error, "The sky is falling!"}                     # this is a tuple with an atom and a string in it.
tup2 = {:success, "Everything is under control."}
tup3 = {:something_else, "Davie Crocket"}

defmodule HandleMessage do
  def check_message({state, msg}) do               # destructure tuple with pattern matching
    case state do                                  # case based on the state atom
      :error -> "An error occured: '#{msg}' 😭"    # if the state is the :error atom -> do this.
      :success -> "Hurray! '#{msg}' 🎉"            # if the state is the :success atom -> do this.
      _ -> "I don't know what to do with this: '#{msg}' 🤷"    # otherwise -> do this.
    end
  end
end

IO.puts(HandleMessage.check_message tup1)
IO.puts(HandleMessage.check_message tup2)
IO.puts(HandleMessage.check_message tup3)

Output:

An error occured: 'The sky is falling!' 😭
Hurray! 'Everything is under control.' 🎉
I don't know what to do with this: 'Davie Crocket' 🤷

Strings

Strings in Elixir are inserted between double quotes and are encoded in UTF-8.

iex(1)> "¿Qué pasa?"
"¿Qué pasa?"

Lists

Lists in Elixir are linked lists and are set in square brackets. Many functions for lists are available in the Enum module. Lists can be of different types.

iex(1)> my_nums_list = [1, 2, 3, 4]
[1, 2, 3, 4]
iex(2)> my_random_stuff_list = [1, "Cheese", :billboard, 33.4]
[1, "Cheese", :billboard, 33.4]
iex(3)> Enum.map(my_nums_list, fn x -> IO.puts(x) end)
1
2
3
4
[:ok, :ok, :ok, :ok]
iex(4)> Enum.map(my_random_stuff_list, fn x -> IO.puts(x) end)
1
Cheese
billboard
33.4
[:ok, :ok, :ok, :ok]

Tuples

From the hexdocs:

Tuples are intended as fixed-size containers for multiple elements. To manipulate a collection of elements, use a list instead. Enum functions do not work on tuples.

Keyword Lists

Maps

Key value data structure.

Functions

Integers

Control Flow

This is an example of a case statement:

tup1 = {:error, "The sky is falling!"}              # this is a tuple with an atom and a string in it.
tup2 = {:success, "Everything is under control."}
tup3 = {:something_else, "Davie Crocket"}

defmodule HandleMessage do
  def check_message({state, msg}) do               # destructure tuple with pattern matching
    case state do                                  # case based on the state atom
      :error -> "An error occured: '#{msg}' 😭"    # if the state is the :error atom -> do this.
      :success -> "Hurray! '#{msg}' 🎉"            # if the state is the :success atom -> do this.
      _ -> "I don't know what to do with this: '#{msg}' 🤷"    # otherwise -> do this.
    end
  end
end

IO.puts(HandleMessage.check_message tup1)
IO.puts(HandleMessage.check_message tup2)
IO.puts(HandleMessage.check_message tup3)

This can also be accomplished with pattern matching and overloading:

tup1 = {:error, "The sky is falling!"}
tup2 = {:success, "Everything is under control."}
tup3 = {:something_else, "Davie Crocket"}

defmodule HandleMessage2 do
  def check_message({:error, msg}) do
    "An error occured: '#{msg}' 😭"
  end

  def check_message({:success, msg}) do
    "Hurray! '#{msg}' 🎉"
  end


  def check_message({_, msg}) do
    "I don't know what to do with this: '#{msg}' 🤷"
  end
end

IO.puts(HandleMessage2.check_message tup1)
IO.puts(HandleMessage2.check_message tup2)
IO.puts(HandleMessage2.check_message tup3)