我可以为任何现有工具导入功能吗？

Question

Let's say i have module with a function having heads with different arity. Is there a way to import this function in another module for all the available arities (without being explicit)?

defmodule Math do
  def plus(a, b) do
  end

  def plus(a, b, c) do
  end

  def plus(a, b, c, d) do
  end
end

defmodule AdditiveCalculator do
  # Explicit import
  import Math, only: [plus: 2, plus: 3, plus: 4]

  # What i'm hoping for
  import Math, only: [plus: :all]
end

Answer 1

As far as I know, there is no such functionality in Elixir.

See here for more details.

---

EDIT:

@tkowal brings up a great point in a comment above. If you're trying to sum variable lists of integers the right approach is to pass the argument as a list of integers and then work with that. Like so:

defmodule T do
  def plus(l) when is_list(l), do: plus(l,0)
  defp plus([], acc), do: acc
  defp plus([item] = l, acc), do: acc + item
  defp plus([head|tail] = l, acc), do: plus(tail, acc+head)
end

Then to use it, call it like this:

T.plus([1,2,3,4])
#=> 10

Answer 2

Your question makes an incorrect assumption about the nature of functions in Elixir. You say you have "a function having heads with different arity" and later "this function".

You don't have a single function with multiple heads. You actually have 3 different functions. Functions are identified by both name and arity. plus/2 , plus/3 and plus/4 may share a name, but they are not the same function. See http://elixir-lang.org/crash-course.html#identifying-functions

This is also why you need to explicitly list them out when specifying the only option on an import . You're importing those 3 distinct functions from the module.