Re: [boost] [review] Convert library

Subject: Re: [boost] [review] Convert library
From: Hartmut Kaiser (hartmut.kaiser_at_[hidden])
Date: 2014-05-26 07:34:28

> >> Thank you for your input. It's much appreciated. From the critical tone
> >> of your post I'll take it you are voting "no". If you did not state it
> >> by accident, then I am happy to do that for you. If you did not state
> it
> >> intentionally, then I think you should as you should not be shying away
> >> from your community responsibilities. :-) Please find my replies below.
> > I intentionally have not cast a vote as I don't have put enough effort
> into
> > a proper review. My main goal was to support Jeroen in his review.
> >
> > In any case, I wanted to mention a possible alternative to the design
> using
> > optional<>. Boost.Filesystem and Boost.Asio give a nice precedent on how
> to
> > construct a library interface supporting both, throwing and non-throwing
> > functions without introducing penalties for either case (based on
> > Boost.System). Using something similar for Convert seems to be a good
> idea.
> >
> 
> I seem to be managing slowly pulling Jeroen onto my "dark" side :-) but
> his "conditional yes" vote so far is on the condition of "the interface
> being simplified for the seemingly simple cases"... which echoes very
> much with your reservations/revulsions ;-) regarding "optional"
> deployment. So, so far, IMO his vote can only responsibly be counted as
> "no"... given that everything else revolves around the proposed
> interface... that you and Jeroen... and quiet a few others are not
> exactly happy with... And that's perfectly fine by me. No drama.
> 
> Thank you for the Boost.Filesystem and Boost.Asio pointers.
> Unfortunately, I am not familiar with the libs. If they indeed handle
> deployment cases similar to those I've been moaning about, then it might
> be wise to postpone going any further with "convert" and study those
> libs for already-existing/established solutions... without
> "optional"-generated controversy... Maybe someone else could shed more
> light on that?...

You usually add a parameter to your function like this:

    // global special error_code object (lives in Boost.System)
    error_code throws;

    void foo(error_code& ec = throws);

then, inside foo() on error you do:

    if (error_happened) {
        if (&ec == &throws)
            // throw exception
        else {
            ec = make_my_error_code();
            return;
        }
    }

Which means, that if you use it as:

    foo();

it will throw on error. However, it will not throw if you write:

    error_code ec;
    foo(ec);
    if (ec) {
        // handle error
    }

HTH
Regards Hartmut
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