discord/deque

---

discord/deque.json

{
  "createdAt": "2017-02-15T21:00:12Z",
  "defaultBranch": "master",
  "description": "Fast bounded deque using two rotating lists.",
  "fullName": "discord/deque",
  "homepage": "",
  "language": "Elixir",
  "name": "deque",
  "pushedAt": "2023-05-31T02:35:12Z",
  "stargazersCount": 156,
  "topics": [
    "datastructures",
    "elixir"
  ],
  "updatedAt": "2025-11-08T14:59:35Z",
  "url": "https://github.com/discord/deque"
}

Deque

Erlang only supports fast prepends to lists while appending requires a full copy. Getting the size of a list is also a O(n) operation. This library implements a deque using two rotating lists to support fast append and prepend as well as O(1) size via an internal counter.

Features

• Bounded size
• Enumerable protocol
• Collectable protocol
• Inspect protocol

Usage

Add it to mix.exs

defp deps do
  [{:deque, "~> 1.0"}]
end

Then use it like other Elixir data structures.

# Deque<[3, 2, 1]>
deque =
  Deque.new(5)
  |> Deque.appendleft(1)
  |> Deque.appendleft(2)
  |> Deque.appendleft(3)

# Deque<[2, 1]>
{3, deque} = Deque.popleft(deque)

# Deque<[6, 7, 8, 9, 10]>
Enum.into(0..10, Deque.new(5))

License

Deque is released under [the MIT License]!(LICENSE). Check [LICENSE]!(LICENSE) file for more information.