Elixir case

?case?允許我們將一個(gè)值與多個(gè)模式進(jìn)行匹配，直到匹配成功：

iex> case {1, 2, 3} do
...>   {4, 5, 6} ->
...>     "This clause won't match"
...>   {1, x, 3} ->
...>     "This clause will match and bind x to 2 in this clause"
...>   _ ->
...>     "This clause would match any value"
...> end
"This clause will match and bind x to 2 in this clause"

如果你想對(duì)已存在的變量進(jìn)行模式匹配，你需要使用操作符：?^?

iex> x = 1
1
iex> case 10 do
...>   ^x -> "Won't match"
...>   _  -> "Will match"
...> end
"Will match"

衛(wèi)語句中允許包含額外的條件：

iex> case {1, 2, 3} do
...>   {1, x, 3} when x > 0 ->
...>     "Will match"
...>   _ ->
...>     "Would match, if guard condition were not satisfied"
...> end
"Will match"

第一條語句在x是正數(shù)時(shí)才能匹配。