Capturing functions

Use & to capture functions from other modules. You can use the captured functions directly as function parameters or within anonymous functions.

Compare the two programs below:

Enum.map(list, fn(x) -> String.capitalize(x) end)

Enum.map(list, &String.capitalize(&1))

Capturing functions without passing any arguments require you to explicitly specify its arity, e.g. &String.capitalize/1:

defmodule Bob do
  def say(message, f \\ &String.capitalize/1) do
    f.(message)
  end
end