Elixir - with

May 4th, 2018

macrowith(args)

Used to combine matching clauses.

iex> opts = %{width: 10, height: 15}
iex> with {:ok, width} <- Map.fetch(opts, :width),
...>      {:ok, height} <- Map.fetch(opts, :height),
...>      do: {:ok, width * height}
{:ok, 150}

If all clauses match, the do block is executed, returning its result. Otherwise the chain is aborted and the non-matched value is returned.

Guards can be used in patterns as well:

iex> users = %{"melany" => "guest", "bob" => :admin}
iex> with {:ok, role} when not is_binary(role) <- Map.fetch(users, "bob"),
...>      do: {:ok, to_string(role)}
{:ok, "admin"}

大宝

乌托邦

xl

Stay hungry, Stay foolish.