Support zipping of any collection, closes #7219

Author: José Valim

lib/elixir/lib/enum.ex

@@ -2718,10 +2718,10 @@ defmodule Enum do
   end
 
   @doc """
-  Zips corresponding elements from a list of enumerables
+  Zips corresponding elements from a finite collection of enumerables
   into one list of tuples.
 
-  The zipping finishes as soon as any enumerable in the given list completes.
+  The zipping finishes as soon as any enumerable in the given collection completes.
 
   ## Examples
 
@@ -2733,10 +2733,11 @@ defmodule Enum do
 
   """
   @spec zip([t]) :: t
+  @spec zip(t) :: t
 
   def zip([]), do: []
 
-  def zip(enumerables) when is_list(enumerables) do
+  def zip(enumerables) do
     Stream.zip(enumerables).({:cont, []}, &{:cont, [&1 | &2]})
     |> elem(1)
     |> :lists.reverse()

lib/elixir/lib/stream.ex

@@ -1091,10 +1091,10 @@ defmodule Stream do
   def zip(left, right), do: zip([left, right])
 
   @doc """
-  Zips corresponding elements from a list of enumerables
+  Zips corresponding elements from a finite collection of enumerables
   into one stream of tuples.
 
-  The zipping finishes as soon as any enumerable in the given list completes.
+  The zipping finishes as soon as any enumerable in the given collection completes.
 
   ## Examples
 
@@ -1105,15 +1105,20 @@ defmodule Stream do
 
   """
   @spec zip([Enumerable.t()]) :: Enumerable.t()
-  def zip(enumerables) when is_list(enumerables) do
+  @spec zip(Enumerable.t()) :: Enumerable.t()
+  def zip(enumerables) do
+    &prepare_zip(enumerables, &1, &2)
+  end
+
+  defp prepare_zip(enumerables, acc, fun) do
     step = &do_zip_step(&1, &2)
 
     enum_funs =
       Enum.map(enumerables, fn enum ->
         {&Enumerable.reduce(enum, &1, step), :cont}
       end)
 
-    &do_zip(enum_funs, &1, &2)
+    do_zip(enum_funs, acc, fun)
   end
 
   # This implementation of do_zip/3 works for any number of
@@ -1128,6 +1133,10 @@ defmodule Stream do
     {:suspended, acc, &do_zip(zips, &1, fun)}
   end
 
+  defp do_zip([], {:cont, acc}, _callback) do
+    {:done, acc}
+  end
+
   defp do_zip(zips, {:cont, acc}, callback) do
     try do
       do_zip_next_tuple(zips, acc, callback, [], [])

lib/elixir/test/elixir/enum_test.exs

@@ -878,10 +878,7 @@ defmodule EnumTest do
     assert Enum.zip([[1]]) == [{1}]
 
     assert Enum.zip([[], [], [], []]) == []
-
-    assert_raise FunctionClauseError, fn ->
-      Enum.zip(%{})
-    end
+    assert Enum.zip(%{}) == []
   end
 end
 

lib/elixir/test/elixir/stream_test.exs

@@ -1099,10 +1099,8 @@ defmodule StreamTest do
     assert Stream.zip([concat, cycle]) |> Enum.to_list() ==
              [{1, :a}, {2, :b}, {3, :c}, {4, :a}, {5, :b}, {6, :c}]
 
-    assert_raise FunctionClauseError, fn ->
-      enum_of_enums = Stream.cycle([[1, 2], [:a, :b]])
-      Stream.zip(enum_of_enums)
-    end
+    assert Stream.chunk_every([0, 1, 2, 3], 2) |> Stream.zip() |> Enum.to_list() ==
+           [{0, 2}, {1, 3}]
   end
 
   test "zip/1 does not leave streams suspended" do