Re: [boost] LEAF has been refactored, it now has a much simplified error handling interface

Subject: Re: [boost] LEAF has been refactored, it now has a much simplified error handling interface
From: Emil Dotchevski (emildotchevski_at_[hidden])
Date: 2019-01-22 21:01:11

On Mon, Jan 21, 2019 at 6:14 PM Sorin Fetche via Boost <
boost_at_[hidden]> wrote:
>
> On Wed, Jan 16, 2019 at 11:51 AM Emil Dotchevski via Boost
> <boost_at_[hidden]> wrote:
> >
> > LEAF is a C++11 error handling library for use in low-latency
environments.
> >
> > - Can be used with or without exception handling.
> >
>
> Is it possible to have a common error handling logic for both error
> codes and exceptions?
> Something like:
>
> leaf::result<T> function_that_may_throw();
> ...
> leaf::handle_all(
>     [i]() -> leaf::result<int> {
>         LEAF_AUTO(r, leaf::exception_to_result<std::exception>([] {
> function_that_may_throw(); }));
>         ...
>         return 0;
>     },
>     [](std::exception const &e) {
>         // Handle exception(s)
>         return 1;
>     },
>     [](custom_error_code ec) {
>         // Handle error code(s)
>         return 2;
>     })
>
> The attached program shows that once leaf::exception_to_result() is
> used, only the exceptions reach the handlers in `handle_all`.

You found a bug, thank you. I had not tested exception_to_result with a
function that returns result<T>, and it incorrectly deduced its return type
as result<result<T>>. I've fixed this in my current working branch,
"feature/error_code", feel free to use that for testing. This new
refactoring pass will make it to "master" in a day probably.

However you're raising an interesting question, should I add explicit
support for handling errors from functions which return result<T> but may
also throw? I don't like exception_to_result very much, I think it can be
useful but the slicing feels a little dangerous. I'll make leaf::try_
detect when the passed try_block returns a result<T>, and handle errors
like leaf::handle_some, in addition to catching exceptions. Thoughts?