The & Operator in Elixir

Writing short helpers functions in Elixir is a natural behavior since Elixir is a functional programming language and thankfully Elixir provides a shortcut to save us time: The & operator.

Create shortcut anonymous functions

Before we get some explanations let’s see what it looks like writing shortcuts anonymous functions.

fn x -> x + 1 end is same as &(&1 + 1)
fn x -> x + x end is same as &(&1 + &1)
fn x, y -> x + y end is same as &(&1 + &2)

Now what happens is that the & operator converts the expression inside the parentheses into an anonymous function where &1, &2 and so on correspond to the parameters given to the function. So &(IO.puts &1 <> " " <> &2) is equivalent to fn hello, world -> IO.puts hello <> " " <> world end. Look at the length of each version and judge by yourself.

A particular use case where the & operator is useful is when we have to pass a function to another function (a common task in Elixir when dealing with data structures).

For example, we want to get each atom from the following list [19, :elixir, 77, :phoenix, 64, {:one, "one"}, :erlang] returned as a string.

list = [19, :elixir, 77, :phoenix, 64, {:one, "one"}, :erlang]
list
 |> Enum.filter(&(is_atom(&1)))
 |> Enum.map(&(to_string(&1)))

When run, the above code outputs: ["elixir", "phoenix", "erlang"] which is exactly what we expected.

Capture named function

Another feature of the & operator is to capture named functions. Capturing mean & can turn a named function into an anonymous function.
The above example could be then refactored capturing is_atom and to_string as following:

list = [19, :elixir, 77, :phoenix, 64, {:one, "one"}, :erlang]
list
  |> Enum.filter(&is_atom/1)
  |> Enum.map(&to_string/1)

And the output remains the same.
This is an optimization since instead of creating an anonymous function and allocating new memory, Elixir maintains a direct reference to the original function. Hope you’ll find this helpful and now that you get it go and save your precious time.

Komlanvi - @doncredas