Vortrags"folien" zu Pattern Matching

pseudo.exs

# Assignment

x = 2

[x, y] = [3, 4]

# perl -e '($one, $two) = (1, 2); print $two;'
# ruby -e "one, two = 1, 2; puts two"



# Assignment++

[x, [y, z]] = [5, [6, 7]]

%{hashes: yay} = %{hashes: "yay"}

%{omg: %{what: [are, you]}, doing: %{please: stahp}} = %{omg: %{what: ["are", "you"]}, doing: %{please: "wtf"}}



# Auch für Strings (Character Listen)

"/" <> path = "/nnev/is/awesome"



# Wozu?

## 1. Assert / Guard

true = false

some_fun = fn -> false end
true = some_fun.()


## 2. Offensichtlich: Variablen rausziehen

{status_code, body, headers} = some_http_call()


## 3. Mit Error Handling:

case some_http_call() do
  {:ok, some_response} -> IO.puts "yay!"
  {:error, some_error} -> IO.puts "oh no!"
  _anything_else       -> IO.puts ":("
end


## 4. Funktionen (statt if)

defmodule Demo do
  def user_data(user,      requester            )
  def user_data(%{id: id}, %{id: id}            ), do: "alles über #{id}"
  def user_data(%{id: id}, %{permission: :admin}), do: "auch alles über #{id}"
  def user_data(%{id: id}, %{id: other_id}      ), do: "wenig über #{id}, weil #{other_id} doof ist"
  def user_data(_user,     _requester           ), do: "nein.jpg"
end

# Demo.user_data(%{id: 1}, %{id: 1})
# Demo.user_data(%{id: 1}, %{id: 2})
# Demo.user_data(%{id: 1}, %{id: 2, permission: :admin})


## 4. Funktionen (defaults)

defmodule Demo2 do
  def absolutify(url_or_path)
  def absolutify("http://" <> _path = url), do: url
  def absolutify("/"       <> path       ), do: "http://nnev.de/#{path}"
end



# Unter der Haube

* Primitive Operationen
* If / Else (bzw. switch)


# Mehr?

https://stackoverflow.com/questions/586362/pattern-matching-implementation