紀錄

pattern_matching = "I am your friend"
"I am your friend"

可以簡單視為解構賦值

"I am your friend" = pattern_matching
"I am your friend"

概念如上述這樣

但一般會像下面這樣使用

{atom, string, charlist, list} = {:i_am_atom, "string", 'charlist', []}
{:i_am_atom, "string", 'charlist', []}

atom === :i_am_atom
true

string === "string"
true

charlist === 'charlist'
true

list === []
true

List 使用

有個觀念要講一下，elixir 的 list，其實是 linked list，所以有特別給一個解構頭與尾的語法

但還是建立在 pattern matching 上做變化

list = ["fisrt", "second", "third"]
["fisrt", "second", "third"]

[head | tail] = list
["fisrt", "second", "third"]

head === "first"
true

tail === ["second", "third"]
true

Function 使用

pattern matching 的性質，可以讓 function 重複命名，依照不同 argument 情況，帶入對應的 function

當參數只有一個的時候

def show_msg(name), do: IO.puts "I'm #{name}. I'm not in a team. I am the team!"

當參數有兩個的時候

def show_msg(name1, name2), do: IO.puts "We are #{name1} and #{name2}. We build the team."

當參數有兩個時候，但有條件

def show_msg(name1, _) when name1 === "Johnson" do
  IO.puts "We build the team! I'm #{name1} and the rest."
end

以上仨 function，可以同時存在於一個 module 裡面

defmodule Meme do
  def show_msg(name), do: IO.puts "I'm #{name}. I'm not in a team. I am the team!"
  def show_msg(name1, name2), do: IO.puts "We are #{name1} and #{name2}. We build the       team."
  def show_msg(name1, _) when name1 === "Johnson" do
    IO.puts "We build the team! I'm #{name1} and the rest."
  end
end