Idiomatic Elixir

Elixir is growing in popularity day by day. Many developers are approaching it with prior patterns and knowledge, building software that works but that doesn’t leverage many features of Erlang and its BEAM runtime. In this talk we’ll go through some examples and learn how to write great Elixir code.

Transcript

1. IDIOMATIC ELIXIR © Erlang Solu,ons Ltd, 2016 1
2. Hello! © Erlang Solu,ons Ltd, 2016 2
3. Claudio Ortolina Head of Elixir at Erlang Solu!ons Ltd. @cloud8421 claudio.ortolina@erlang-solu!ons.com © Erlang Solu,ons Ltd, 2016 3
4. IDIOMATIC ELIXIR © Erlang Solu,ons Ltd, 2016 4
5. IDIOMATIC ELIXIR © Erlang Solu,ons Ltd, 2016 5
6. FLEXIBLE ELIXIR © Erlang Solu,ons Ltd, 2016 6
7. DEFINITION 1 flexible adjec!ve - /ˈflek.sə.bəl/ • Able to change or be changed easily according to the situa!on • Able to bend or to be bent easily without breaking 1 h!p:/ /dic"onary.cambridge.org/dic"onary/english/flexible © Erlang Solu,ons Ltd, 2016 7
8. WARNING: CODE AHEAD © Erlang Solu,ons Ltd, 2016 8
9. 1. HANDLING VOLATILE DATA © Erlang Solu,ons Ltd, 2016 9
10. CACHE STORE defmodule CacheStore do @type key :: term @type value :: term @type reason :: term @spec get(key) :: {:ok, value} | {:error, reason} @spec set(key, value) :: :ok @spec start_link() :: {:ok, pid} | {:error, reason} end © Erlang Solu,ons Ltd, 2016 10
11. v1: AGENT © Erlang Solu,ons Ltd, 2016 11
12. defmodule MyApp do def start(_type, _args) do children = [ worker(CacheStore, []) ] ... end end defmodule CacheStore do def start_link() do initial = fn() -> %{} end Agent.start_link(initial, name: __MODULE__) end end © Erlang Solu,ons Ltd, 2016 12
13. defmodule CacheStore do def set(key, val) do Agent.cast(__MODULE__, fn(store) -> Dict.put(store, key, val) end) end def get(key) do Agent.get(__MODULE__, fn(store) -> case Dict.get(store, key) do :error -> {:error, :not_found} value -> {:ok, value} end end) end end © Erlang Solu,ons Ltd, 2016 13
14. ! SIMPLE © Erlang Solu,ons Ltd, 2016 14
15. ! STRICTLY CONSISTENT © Erlang Solu,ons Ltd, 2016 15
16. ! ONE OPERATION AT A TIME © Erlang Solu,ons Ltd, 2016 16
17. ! IF AGENT CRASHES, DATA IS LOST © Erlang Solu,ons Ltd, 2016 17
18. v2: GenServer + ETS © Erlang Solu,ons Ltd, 2016 18
19. GenServer • Generic server behaviour • Used to model client-server rela!onship • Server holds data and api to access/mutate it • Used to implement Agent © Erlang Solu,ons Ltd, 2016 19
20. ETS • Erlang Term Storage • Built-in • Large, in-memory data storage • Constant !me access © Erlang Solu,ons Ltd, 2016 20
21. defmodule CacheStore do use GenServer def start_link do GenServer.start_link(__MODULE__, [], name: __MODULE__) end def init([]) do :ets.new(__MODULE__, [:named_table, :bag, :public, read_concurrency: true]) {:ok, []} end end © Erlang Solu,ons Ltd, 2016 21
22. defmodule CacheStore do ... def set(key, value) do GenServer.cast(__MODULE__, {:set, key, value}) end def handle_cast({:set, key, value}, state) do true = :ets.insert(__MODULE__, {key, value}) {:noreply, state} end end © Erlang Solu,ons Ltd, 2016 22
23. defmodule CacheStore do ... def get(key) do case :ets.lookup(__MODULE__, key) do [] -> {:error, :not_found} [{^key, result}] -> {:ok, result} end end def handle_cast({:set, key, value}, state) do true = :ets.insert(__MODULE__, {key, value}) {:noreply, state} end end © Erlang Solu,ons Ltd, 2016 23
24. ! CONCURRENT WRITES AND READS © Erlang Solu,ons Ltd, 2016 24
25. ! EVENTUALLY CONSISTENT © Erlang Solu,ons Ltd, 2016 25
26. ! IF SERVER CRASHES, DATA IS GONE © Erlang Solu,ons Ltd, 2016 26
27. v3: GenServer + ETS + App © Erlang Solu,ons Ltd, 2016 27
28. defmodule CacheStore do def create_cache_table do :ets.new(__MODULE__, [:named_table, :duplicate_bag, :public, read_concurrency: true]) end end © Erlang Solu,ons Ltd, 2016 28
29. defmodule MyApp do def start(_type, _args) do # The app process owns the table now CacheStore.create_cache_table children = [ worker(CacheStore, []) ] ... end end © Erlang Solu,ons Ltd, 2016 29
30. ! ONLY AN APP CRASH CAN AFFECT THE CACHED DATA © Erlang Solu,ons Ltd, 2016 30
31. 2. LONG RUNNING PROCESSES © Erlang Solu,ons Ltd, 2016 31
32. GAME PROCESS • Game session in a process • Data is self-contained • Exposes expensive opera!ons © Erlang Solu,ons Ltd, 2016 32
33. v1: GenServer © Erlang Solu,ons Ltd, 2016 33
34. defmodule Game do use GenServer defmodule State do defstruct score: 0, players: [], ... end def player_avatars(pid) do GenServer.call(pid, :player_avatars) end def handle_call(:player_avatars, _from, state) do ids = Enum.map(state.players, fn(p) -> p.id end) {:ok, avatars} = slow_fetch_urls(ids) {:reply, avatars, state} end end © Erlang Solu,ons Ltd, 2016 34
35. ! IT WORKS © Erlang Solu,ons Ltd, 2016 35
36. ! WHILE FETCHING, THE GAME IS BLOCKED © Erlang Solu,ons Ltd, 2016 36
37. ! IF FETCH FAILS, THE GAME DIES © Erlang Solu,ons Ltd, 2016 37
38. 2. GenServer.reply © Erlang Solu,ons Ltd, 2016 38
39. defmodule Game do ... def player_avatars(pid) do GenServer.call(pid, :player_avatars) end def handle_call(:player_avatars, from, state) do spawn(fn() -> ids = Enum.map(state.players, fn(p) -> p.id end) {:ok, avatars} = slow_fetch_urls(ids) GenServer.reply(from, avatars) end) {:noreply, state} end end © Erlang Solu,ons Ltd, 2016 39
40. ! FETCH HAPPENS IN DIFFERENT PROCESS © Erlang Solu,ons Ltd, 2016 40
41. ! WHEN FETCH FAILS, GAME IS UNAFFECTED © Erlang Solu,ons Ltd, 2016 41
42. ! SAME GUARANTEES FOR THE CALLER © Erlang Solu,ons Ltd, 2016 42
43. ! EVENTUAL CONSISTENCY © Erlang Solu,ons Ltd, 2016 43
44. 3. FUNCTIONAL CHAINS © Erlang Solu,ons Ltd, 2016 44
45. DIGEST USER INPUT • Incoming data • Whitelist, validate, store • Each step may fail • Computa!on must return a value © Erlang Solu,ons Ltd, 2016 45
46. v1: PURE PIPELINE © Erlang Solu,ons Ltd, 2016 46
47. defmodule CreateUser do @allowed_params ~w(email username) def run(params) do params |> whitelist |> validate |> store end def whitelist(params) do Map.take(params, @allowed_params) end end © Erlang Solu,ons Ltd, 2016 47
48. defmodule MyApp.UserController do def create(params) do case CreateUser.run(params) do {:ok, _user} -> resp(conn, 201, :created) _error -> resp(conn, 406, :malformed) end end end © Erlang Solu,ons Ltd, 2016 48
49. ! WORKS GREAT FOR GOLDEN PATH © Erlang Solu,ons Ltd, 2016 49
50. ! FAILS WITH ARGUMENT ERRORS © Erlang Solu,ons Ltd, 2016 50
51. v2: TRY..RESCUE © Erlang Solu,ons Ltd, 2016 51
52. defmodule CreateUser do @allowed_params ~w(email username) def run(params) do try do params |> whitelist |> validate |> store rescue error -> error end end def whitelist(params) do Map.take(params, @allowed_params) end end © Erlang Solu,ons Ltd, 2016 52
53. ! TRY..RESCUE HIDES ERRORS © Erlang Solu,ons Ltd, 2016 53
54. ! ALL FAILURES ARE TREATED THE SAME © Erlang Solu,ons Ltd, 2016 54
55. v3: WITH MACRO © Erlang Solu,ons Ltd, 2016 55
56. defmodule CreateUser do @allowed_params ~w(email username) def run(params) do with {:ok, whitelisted} <- whitelist(params), {:ok, valid} <- validate(whitelisted) do store(valid) else error -> error end end def whitelist(params) do {:ok, Map.take(params, @allowed_params)} end end © Erlang Solu,ons Ltd, 2016 56
57. ! CLEARLY EXPRESS WHAT CAN FAIL © Erlang Solu,ons Ltd, 2016 57
58. ! CONTROL OVER FAILURE CASES © Erlang Solu,ons Ltd, 2016 58
59. ! EXCEPTIONS DIFFERENT FROM ERRORS © Erlang Solu,ons Ltd, 2016 59
60. ! NEED TO "TAG" RETURN VALUES © Erlang Solu,ons Ltd, 2016 60
61. FLEXIBLE ELIXIR © Erlang Solu,ons Ltd, 2016 61
62. RICH STANDARD LIBRARY © Erlang Solu,ons Ltd, 2016 62
63. CHOOSE WHO OWNS DATA © Erlang Solu,ons Ltd, 2016 63
64. CHOOSE WHO RUNS FUNCTIONS © Erlang Solu,ons Ltd, 2016 64
65. CHOOSE FAILURE SEMANTICS © Erlang Solu,ons Ltd, 2016 65
66. THANKS! © Erlang Solu,ons Ltd, 2016 66
67. Claudio Ortolina Head of Elixir at Erlang Solu!ons Ltd. @cloud8421 claudio.ortolina@erlang-solu!ons.com © Erlang Solu,ons Ltd, 2016 67