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Fix Enum.take for Stream.chunk_by #3042

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Fix Enum.take for Stream.chunk_by #3042

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4 changes: 4 additions & 0 deletions lib/elixir/lib/stream.ex
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Original file line number Diff line number Diff line change
Expand Up @@ -197,6 +197,10 @@ defmodule Stream do
{:cont, acc}
end

defp do_chunk_by(acc({_, 1}, _, _) = acc, _f1) do
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Unfortunately this fix is not correct. We cannot access the accumulator state because the take value can be nested inside other states or it could just mean whatever. :)

{:cont, acc}
end

defp do_chunk_by(acc(h, {buffer, _}, t), f1) do
cont_with_acc(f1, :lists.reverse(buffer), h, nil, t)
end
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27 changes: 16 additions & 11 deletions lib/elixir/test/elixir/stream_test.exs
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Original file line number Diff line number Diff line change
Expand Up @@ -41,8 +41,7 @@ defmodule StreamTest do
end

test "chunk/2, chunk/3 and chunk/4" do
assert Stream.chunk([1, 2, 3, 4, 5], 2) |> Enum.to_list ==
[[1, 2], [3, 4]]
assert Stream.chunk([1, 2, 3, 4, 5], 2) |> Enum.to_list == [[1, 2], [3, 4]]
assert Stream.chunk([1, 2, 3, 4, 5], 2, 2, [6]) |> Enum.to_list ==
[[1, 2], [3, 4], [5, 6]]
assert Stream.chunk([1, 2, 3, 4, 5, 6], 3, 2) |> Enum.to_list ==
Expand All @@ -55,6 +54,7 @@ defmodule StreamTest do
[[1, 2, 3], [4, 5, 6]]
assert Stream.chunk([1, 2, 3, 4, 5], 4, 4, 6..10) |> Enum.to_list ==
[[1, 2, 3, 4], [5, 6, 7, 8]]
assert 1..10 |> Stream.chunk(2) |> Enum.take(2) == [[1, 2], [3, 4]]
end

test "chunk/4 is zippable" do
Expand All @@ -80,18 +80,23 @@ defmodule StreamTest do
stream = Stream.chunk_by([1, 2, 2, 3, 4, 4, 6, 7, 7], &(rem(&1, 2) == 1))

assert is_lazy(stream)
assert Enum.to_list(stream) ==
[[1], [2, 2], [3], [4, 4, 6], [7, 7]]
assert stream |> Stream.take(3) |> Enum.to_list ==
[[1], [2, 2], [3]]
assert Enum.to_list(stream) == [[1], [2, 2], [3], [4, 4, 6], [7, 7]]
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Please avoid changing style of other assertions as it makes it hard to see what is being changed as part of this change. :)

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Sorry about that, I just went through each test and add take assertion where it missed, to prevent such things in future. Below I added line 85.

assert stream |> Stream.take(3) |> Enum.to_list == [[1], [2, 2], [3]]
assert stream |> Enum.take(2) == [[1], [2, 2]]
end

test "chunk_by/2 is zippable" do
stream = Stream.chunk_by([1, 2, 2, 3], &(rem(&1, 2) == 1))
list = Enum.to_list(stream)

assert Enum.zip(list, list) == Enum.zip(stream, stream)
end

test "chunk_by/4 is haltable" do
assert 1..10 |> Stream.take(6) |> Stream.chunk_by(&(rem(&1, 3) == 0))
|> Stream.take(2) |> Enum.to_list == [[1, 2], [3]]
end

test "concat/1" do
stream = Stream.concat([1..3, [], [4, 5, 6], [], 7..9])
assert is_function(stream)
Expand Down Expand Up @@ -527,6 +532,7 @@ defmodule StreamTest do
stream = Stream.scan(1..5, &(&1 + &2))
assert is_lazy(stream)
assert Enum.to_list(stream) == [1,3,6,10,15]
assert Enum.take(stream, 3) == [1,3,6]
assert Stream.scan([], &(&1 + &2)) |> Enum.to_list == []
end

Expand Down Expand Up @@ -650,11 +656,10 @@ defmodule StreamTest do
end

test "uniq/1" do
assert Stream.uniq([1, 2, 3, 2, 1]) |> Enum.to_list ==
[1, 2, 3]

assert Stream.uniq([{1, :x}, {2, :y}, {1, :z}], fn {x, _} -> x end) |> Enum.to_list ==
[{1,:x}, {2,:y}]
assert Stream.uniq([1, 2, 3, 2, 1]) |> Enum.to_list == [1, 2, 3]
assert Stream.uniq([1, 2, 3, 2, 1]) |> Enum.take(2) == [1, 2]
assert Stream.uniq([{1, :x}, {2, :y}, {1, :z}], fn {x, _} -> x end)
|> Enum.to_list == [{1,:x}, {2,:y}]
end

test "zip/2" do
Expand Down