Elixir code (and the underlying Erlang libraries) can raise a second kind of error. These are generated when a process calls error, exit, or throw. All three take a parameter, which is available to the catch handler.
Here’s an example:
| | defmodule Catch do |
| | |
| | def start(n) do |
| | try do |
| | incite(n) |
| | catch |
| | :exit, code -> "Exited with code #{inspect code}" |
| | :throw, value -> "throw called with #{inspect value}" |
| | what, value -> "Caught #{inspect what} with #{inspect value}" |
| | end |
| | end |
| | |
| | |
| | defp incite(1) do |
| | exit(:something_bad_happened) |
| | end |
| | |
| | defp incite(2) do |
| | throw {:animal, "wombat"} |
| | end |
| | |
| | defp incite(3) do |
| | :erlang.error "Oh no!" |
| | end |
| | end |
Calling the start function with 1, 2, or 3 will cause an exit, a throw, or an error to be thrown. Just to illustrate wildcard pattern matching, we handle the last case by matching any type into the variable what.
| | iex> c("catch.ex") |
| | [Catch] |
| | iex> Catch.start 1 |
| | "Exited with code :something_bad_happened" |
| | iex> Catch.start 2 |
| | "throw called with {:animal,\"wombat\"}" |
| | iex> Catch.start 3 |
| | "Caught :error with \"Oh no!\"" |