Re: [boost] expected<T, E...> (Was: [outcome] High level summary of review feedback accepted so far)

Subject: Re: [boost] expected<T, E...> (Was: [outcome] High level summary of review feedback accepted so far)
From: Peter Dimov (lists_at_[hidden])
Date: 2017-06-04 16:05:56

Vicente J. Botet Escriba wrote:
> Le 04/06/2017 à 17:42, Peter Dimov via Boost a écrit :
> > Vicente J. Botet Escriba wrote:
> >> >    enum unscoped_error
> >> >    {
> >> >        unscoped_other_error = 7
> >> >    };
> >> >
> >> >    expected<double, unscoped_error> test()
> >> >    {
> >> >        return unscoped_other_error; // returns 7.0
> >> >    }
> >
> > ...
> >
> >> unexpected_type<E> is explicitly constructible from E. expected<T, E> 
> >> is implicitly constructible from unexpected_type<E>. This avoid this 
> >> kind of ambiguities.
> >
> > Could you please try this code with your implementation?
>
> It will work as yours. My concern is that this is not what we want, isn't 
> it?

It's not, but what you say above - "this avoid this kind of ambiguities" - 
created the impression that you think that it isn't a problem.

As I see it, this can be avoided by either making the constructor from T 
explicit as well, or by making the constructor from E implicit as well.