exception-handling - Erlang 错误处理哲学 - case vs throw

Question

我正在用 Erlang 编写 REST 服务，需要先验证接收到的数据，然后再将其传递给其他内部函数进行进一步处理；为了做到这一点，我目前正在使用嵌套 case像这样的表达:

case all_args_defined(Args) of
    true ->
        ActionSuccess = action(Args),

        case ActionSuccess of
            {ok, _} -> ...;
            {fail, reason} -> {fail, reason}
        end,
    _ ->
        {fail, "args not defined"}
end,
...

我意识到这有点难看，但这样我就可以提供详细的错误消息。此外，我不认为通常的让它崩溃的哲学在这里适用 - 我不希望我的 REST 服务崩溃并在每次有人向它抛出无效参数时重新启动。

但是，我正在考虑放弃所有这些 cases赞成一把伞 try/catch拦截任何 badmatch错误 - 这行得通吗？

fun() ->
    true = all_args_defined(Args),
    {ok, _} = action(Args).

%% somewhere else
catch fun().

Answer 1

由于您想要实现的是错误报告，因此您应该围绕操作的执行和结果的报告来构建事物。也许是这样的:

  execute(Action, Args) ->
    try
      check_args(Args),
      Result = action(Action, Args),
      send_result(Result)
    catch
      throw:{fail, Reason} ->
        report_error(Reason);
      ExceptionClass:Term ->
        %% catch-all for all other unexpected exceptions
        Trace = erlang:get_stacktrace(),
        report_error({crash, ExceptionClass, Term, Trace})
    end.

  %% all of these throw {fail, Reason} if they detect something fishy
  %% and otherwise they return some value as result (or just crash)
  action(foo, [X1, X2]) -> ...;
  action(foo, Args) -> throw({fail, {bad_arity, foo, 2, Args}});
  action(...) -> ...

  %% this handles the formatting of all possible errors 
  report_error({bad_arity, Action, Arity, Args}) ->
    send_error(io_lib:format("wrong number of arguments for ~w: "
                             "expected ~w, but got ~w",
                             [Action, Arity, length(Args)]));
  report_error(...) -> ...;
  report_error({crash, Class, Term, Trace}) ->
    send_error(io_lib:format("internal error: "
                             "~w:~w~nstacktrace:~n~p~n",
                             [Class, Term, Trace])).