Re: [boost] Noexcept

Subject: Re: [boost] Noexcept
From: Emil Dotchevski (emildotchevski_at_[hidden])
Date: 2017-06-12 20:28:10

On Mon, Jun 12, 2017 at 1:15 PM, Andrzej Krzemienski via Boost <
boost_at_[hidden]> wrote:

> 2017-06-12 20:07 GMT+02:00 Emil Dotchevski via Boost <
> boost_at_[hidden]>
> :
>
> > On Mon, Jun 12, 2017 at 2:42 AM, Niall Douglas via Boost <
> > boost_at_[hidden]> wrote:
> >
> > > On 12/06/2017 09:22, Emil Dotchevski via Boost wrote:
> > > > The lively debates during the Outcome review show that there is a
> great
> > > > deal of interest in solving the problem of error handling in
> > environments
> > > > where C++ exception handling is unavailable.
> > > >
> > > > Noexcept is a new C++11 library that implements a different approach
> to
> > > > solving the same problem. Any feedback is welcome.
> > > >
> > > > https://zajo.github.io/boost-noexcept/
> > >
> > > The use of functional throw(), try() and catch() was a design approach
> > > rejected very early by me and most who have looked into this problem.
> > >
> > > Nobody wants to reimplement via a library exception handling with
> > > exceptions disabled. It's an impoverished experience, and leads to
> > > brittle code.
> >
> >
> > Can you elaborate? My understanding is that the problem with exception
> > handling is the unpredictability of the performance you'll get. Noexcept
> > directly addresses that issue by not introducing the unpredictability of
> > its own return type which may or may not get optimized.
> >
> > It also removes the redundancy of requiring types which already have a
> > useful empty state to be wrapped into something like outcome<>. Nobody
> > would return optional<FILE *> from a function that may fail, they'll just
> > return FILE */nullptr. Returning outcome<FILE *> is similarly redundant
> and
> > possibly inefficient.
> >
> >
> > > Just enable C++ exceptions if you want exceptions.
> > >
> >
> > I agree, the question is what to do if you can't.
> >
>
> There is a number of expectations people have or might have form
> error-handling framework:
>
> 1. Predictable times.
> 2. When I forget to check for error, the computation should not silently
> proceed.
> 3. Not polluting the function return type
> 4. Explicit control flows.
> 5. No explicit control flows.
> 6. Neutrality for some functions, elspecially those extern "C".
> 7. Being fast.
> 8. Being able to carry any payload.
>
> Obviously, a framework cannot guarantee all of these, and trade-offs need
> to be made. One thing that both exceptions, and outcome<>/expected<> have
> is #2: when you forget that the function might fail, and it fails, the
> dependent functions will not get called.

What do you mean "dependent functions"?

> In case of exceptions this is
> owing to stack unwinding. In case of outcome, it is because the program
> will not compile.

Can you post an actual example so we're not talking in the abstract?