Why are error codes being deprecated?

[ruipacheco]

I've noticed this in the file io_context.ipp:

io_context::count_type io_context::run()
{
  asio::error_code ec;
  count_type s = impl_.run(ec);
  asio::detail::throw_error(ec);
  return s;
}

#if !defined(ASIO_NO_DEPRECATED)
io_context::count_type io_context::run(asio::error_code& ec)
{
  return impl_.run(ec);
}
#endif // !defined(ASIO_NO_DEPRECATED)

Why is the use of std::error_code being deprecated?

[ruipacheco]

I wonder if this is linked to issue 143?

[vinniefalco]

It isn't all error codes being deprecated but rather, some functions are now exclusively indicating errors using exceptions. This makes sense. Remember that functions which have error_code& in their signature can still throw exceptions, the most common one being std::bad_alloc. What I think this change signifies is that io_context::run will not return errors which do not indicate exceptional circumstances.

You also see this with basic_io_object::cancel. In my opinion, this is a good change.

[ruipacheco]

What happens to code that compiles with -fno-exceptions?

…

On 3 May 2018, at 19:29, Vinnie Falco ***@***.***> wrote: It isn't all error codes being deprecated but rather, some functions are now exclusively indicating errors using exceptions. This makes sense. Remember that functions which have error_code& in their signature can still throw exceptions, the most common one being std::bad_alloc. What I think this change signifies is that io_context::run will not return errors which do not indicate exceptional circumstances. You also see this with basic_io_object::cancel. In my opinion, this is a good change. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#302 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAfK738pj_--VaWg-L2XuYLHc2iAev7Hks5tuz5dgaJpZM4TuVaw>.

[vinniefalco]

What happens to code that compiles with -fno-exceptions?

That's up to you. You should define ASIO_NO_EXCEPTIONS=1 and then provide your own implementation of throw_exception that does whatever you want:

https://github.com/chriskohlhoff/asio/blob/master/asio/include/asio/detail/throw_exception.hpp#L33

[ruipacheco]

This seems to contradict the comment below: // Only define the throw_exception function when exceptions are enabled. // Otherwise, it is up to the application to provide a definition of this // function.

…

On 3 May 2018, at 19:35, Vinnie Falco ***@***.***> wrote: What happens to code that compiles with -fno-exceptions? That's up to you. You should define ASIO_NO_EXCEPTIONS=1 and then provide your own implementation of throw_exception that does whatever you want: https://github.com/chriskohlhoff/asio/blob/master/asio/include/asio/detail/throw_exception.hpp#L33 <https://github.com/chriskohlhoff/asio/blob/master/asio/include/asio/detail/throw_exception.hpp#L33> — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#302 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAfK70q8p1uAhZy8hEEyN3XZfrTH1jUBks5tuz_pgaJpZM4TuVaw>.

[vinniefalco]

This seems to contradict the comment below:

I think you're reading it wrong. "Only define the throw_exception function" applies to the asio implementation not yours. In other words, if exceptions are enabled (ASIO_NO_EXCEPTIONS is not defined) then Asio will define the function throw_exception. Otherwise, you will have to define it.

If you use -fno-exceptions then you also need to define ASIO_NO_EXCEPTIONS=1.

[ruipacheco]

Got it, thanks!

…

On 3 May 2018, at 19:38, Vinnie Falco ***@***.***> wrote: This seems to contradict the comment below: I think you're reading it wrong. "Only define the throw_exception function" applies to the asio implementation not yours. In other words, if exceptions are enabled (ASIO_NO_EXCEPTIONS is not defined) then Asio will define the function throw_exception. Otherwise, you will have to define it. If you use -fno-exceptions then you also need to define ASIO_NO_EXCEPTIONS=1. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#302 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAfK71ut2GY9SvSQAAVwGclTHJw2-KaFks5tu0CUgaJpZM4TuVaw>.

[vinniefalco]

@chriskohlhoff

If we change

"Only define the throw_exception function..." 

to

"Asio will only define the throw_exception function..."

it could be more clear.

[ruipacheco]

Can you provide any examples of a custom definition of throw_exception when ASIO_NO_EXCEPTIONS is defined?

[vinniefalco]

template <typename Exception>
void throw_exception(const Exception& e)
{
    std::cerr << "Your app just shit the bed, because: " << e.what() << std::endl;
    std::terminate();
}

Alternatively you could log to a file, launch another process, etc... many choices. Just not throw.

[vinniefalco]

Has this issue been resolved?

[ruipacheco]

Done!