Pattern matching in Elixir by example - Alexander Khokhlov
0 likes329 views
Pattern matching in Elixir allows variables to be bound to values in a structure like a tuple, map, or list. It checks for structural equality rather than referential equality. Some key aspects of pattern matching include: variables can be rebound but not reassigned, patterns can match nested data structures, and functions can have multiple clauses to handle different patterns. Pattern matching is used throughout Elixir for control flow, case expressions, with expressions, and more.
![iex > {:ok, value} = {:ok, "Successful!"}
{:ok, "Successful!"}
iex > value
“Successful!”
iex > {:ok, value} = {:error, "Shit:("}
** (MatchError) no match of right hand side
value: {:error, “Shit:(“}
iex > {:ok, value} = [:ok, "Success"]
** (MatchError) no match of right hand side
value: [:ok, "Success"]](https://image.slidesharecdn.com/elixir-meetup-presentation-171228164857/85/Pattern-matching-in-Elixir-by-example-Alexander-Khokhlov-14-320.jpg)
![iex > list = [1, 2, 3]
[1, 2, 3]
iex > [1 | tail] = list
[1, 2, 3]
iex > tail
[2, 3]
iex > [2 | _] = list
** (MatchError) no match of right hand side
value: [1, 2, 3]
iex > [head | tail] = list
[1, 2, 3]
iex > head
1](https://image.slidesharecdn.com/elixir-meetup-presentation-171228164857/85/Pattern-matching-in-Elixir-by-example-Alexander-Khokhlov-17-320.jpg)
![def hello(:point)
def hello("Alex" <> _)
def hello([name1, name2 | _])
def hello(%{first_name: name})
def hello(_)
def hello(_name)](https://image.slidesharecdn.com/elixir-meetup-presentation-171228164857/85/Pattern-matching-in-Elixir-by-example-Alexander-Khokhlov-22-320.jpg)
![def hello(%x{} = person) when x in [Person] do
IO.puts("Hello, #{person.first_name}")
end](https://image.slidesharecdn.com/elixir-meetup-presentation-171228164857/85/Pattern-matching-in-Elixir-by-example-Alexander-Khokhlov-26-320.jpg)
![def create(params) do
case validate_name(params["name"]) do
{:ok, name} ->
case validate_email(params["email"]) do
{:ok, email} ->
create_db_record(name, email)
{:error, message} ->
conn |> put_flash(:error, "Wrong email: #{message}")
|> redirect(to: "/")
end
{:error, message} ->
conn |> put_flash(:error, "Wrong name: #{message}")
|> redirect(to: "/")
end
end](https://image.slidesharecdn.com/elixir-meetup-presentation-171228164857/85/Pattern-matching-in-Elixir-by-example-Alexander-Khokhlov-32-320.jpg)
![def create(params) do
with {:ok, name} <- validate_name(params["name"]),
{:ok, email} <- validate_email(params["email"])
do
create_db_record(name, email)
else
{:name_error, message} ->
conn |> put_flash(:error, "Wrong name: #{message}") |>
redirect(to: "/")
{:email_error, message} ->
conn |> put_flash(:error, "Wrong email: #{message}") |
> redirect(to: "/")
end
end](https://image.slidesharecdn.com/elixir-meetup-presentation-171228164857/85/Pattern-matching-in-Elixir-by-example-Alexander-Khokhlov-33-320.jpg)
Pattern matching in Elixir by example - Alexander Khokhlov
- 1. Александр Хохлов @apoint Pattern matching in Elixir by example
- 3. TL;DR
- 6. История
- 7. Erlang The Movie II: The Sequel https://www.youtube.com/watch?v=rRbY3TMUcgQ https://img00.deviantart.net/de6b/i/2011/044/b/9/erlang_the_movie_by_mcandre-d39hupa.png
- 10. iex > a = 1 1 iex > 1 = a 1 iex > 2 = a ** (MatchError) no match of right hand side value: 1
- 11. Переменные можно связывать заново (rebind)
- 12. iex > b = 2 2 iex > b = 3 3 iex > ^b = 4 ** (MatchError) no match of right hand side value: 4 iex > ^b = 3 3
- 14. iex > {:ok, value} = {:ok, "Successful!"} {:ok, "Successful!"} iex > value “Successful!” iex > {:ok, value} = {:error, "Shit:("} ** (MatchError) no match of right hand side value: {:error, “Shit:(“} iex > {:ok, value} = [:ok, "Success"] ** (MatchError) no match of right hand side value: [:ok, "Success"]
- 15. iex > %{key: value} = %{key: “hash value"} %{key: “hash value"} iex > value “hash value” iex > %{key1: value} = %{key1: "value1", key2: "value2"} %{key1: "value1", key2: "value2"} iex > value “value1" iex > key = :key1 :key1 iex > %{^key => value} = %{key1: "value1", key2: "value2"} %{key1: "value1", key2: "value2"} iex > value "value1"
- 16. А еще списки
- 17. iex > list = [1, 2, 3] [1, 2, 3] iex > [1 | tail] = list [1, 2, 3] iex > tail [2, 3] iex > [2 | _] = list ** (MatchError) no match of right hand side value: [1, 2, 3] iex > [head | tail] = list [1, 2, 3] iex > head 1
- 18. Функции
- 20. iex > defmodule Hello do ... > def hello(name) do ... > "Hello, #{name}" ... > end ... > end … skipped … iex > Hello.hello("point") "Hello, point"
- 21. iex > defmodule Hello do ... > def hello(:point) do ... > "Greeting, my lord" ... > end ... > def hello(name) do ... > "Hello, #{name}" ... > end ... > end iex > Hello.hello(:point) "Greeting, my lord" iex > Hello.hello("John") "Hello, John"
- 22. def hello(:point) def hello("Alex" <> _) def hello([name1, name2 | _]) def hello(%{first_name: name}) def hello(_) def hello(_name)
- 23. Хардкор
- 25. iex > defmodule Person do ... > defstruct first_name: "", last_name: "" ... > end iex > def hello(%Person{} = person) do ... > IO.puts("Hello, #{person.first_name}") ... > end iex > Hello.hello(%Person{first_name: "Arthur", last_name: "Dent"}) Hello, Arthur def hello(%Person{first_name: first_name})
- 26. def hello(%x{} = person) when x in [Person] do IO.puts("Hello, #{person.first_name}") end
- 27. defmodule Person do defstruct age: 0 end defmodule Greeting do def hello(%{age: age}) when 6 < age and age < 12, do: "Hiya" def hello(%{age: age}) when age in 12..18, do: "Whatever" def hello(%{age: age}) when 60 < age, do: “You kids get off my lawn" def hello(_), do: "Hello" end https://hexdocs.pm/elixir/master/guards.html
- 28. def hello() do result = case {:ok, "Successful!"} do {:ok, result} -> result {:error} -> "Shit:(" _ -> "Catch all" end # result == "Successful!" end
- 29. defmodule Factorial do def of(0), do: 1 def of(n) when n > 0 do n * of(n - 1) end end iex > Factorial.of(10) 3628800
- 30. defmodule ImageTyper do @png_signature <<137::size(8), 80::size(8), 78::size(8), 71::size(8), 13::size(8), 10::size(8), 26::size(8), 10::size(8)>> @jpg_signature <<255::size(8), 216::size(8)>> def type(<<@png_signature, rest::binary>>), do: :png def type(<<@jpg_signature, rest::binary>>), do: :jpg def type(_), do :unknown end
- 32. def create(params) do case validate_name(params["name"]) do {:ok, name} -> case validate_email(params["email"]) do {:ok, email} -> create_db_record(name, email) {:error, message} -> conn |> put_flash(:error, "Wrong email: #{message}") |> redirect(to: "/") end {:error, message} -> conn |> put_flash(:error, "Wrong name: #{message}") |> redirect(to: "/") end end
- 33. def create(params) do with {:ok, name} <- validate_name(params["name"]), {:ok, email} <- validate_email(params["email"]) do create_db_record(name, email) else {:name_error, message} -> conn |> put_flash(:error, "Wrong name: #{message}") |> redirect(to: "/") {:email_error, message} -> conn |> put_flash(:error, "Wrong email: #{message}") | > redirect(to: "/") end end
- 35. defmodule MyAppWeb.PageController do action_fallback MyAppWeb.FallbackController def show(params) do with {:ok, username} <- get_username(params), {:ok, cms_page} <- CMS.get_page(username, params) do render(conn, "show.html", page: page) end end end defmodule MyAppWeb.FallbackController do def call(conn, {:username_error, message}) do conn |> put_flash(:error, "Wrong usernname: #{message}") |> redirect(to: "/") end def call(conn, {:cms_page_not_found, message}) do conn |> put_flash(:error, "Page not found: #{message}") |> redirect(to: "/") end end
- 36. defmodule NotsappWeb.ProjectsFallbackController do use Phoenix.Controller def call(conn, _) do conn |> put_status(:not_found) |> put_layout(false) |> render(NotsappWeb.ErrorView, :”501") end end