Re: [boost] [system] Would it be possible to trial a breaking change to Boost.System and see what happens?

Subject: Re: [boost] [system] Would it be possible to trial a breaking change to Boost.System and see what happens?
From: Peter Dimov (lists_at_[hidden])
Date: 2018-01-12 19:03:25

Andrey Semashev wrote:
>    void foo(error_code& err)
>    {
>      // Do stuff...
>      err = make_error_code(success); // error_code(0, my_category)
>    }
...
> I suppose, you could argue that I could avoid `err` initialization in 
> `foo`, but that is a matter of taste and whether you want to rely on the 
> initial state of `err` on entry into `foo`.

No, I'm not going to argue that; it's idiomatic to clear `err` on entry:

void foo( error_code& err )
{
    err.clear();
    // do stuff
}

with the alternative

    err.assign( 0, err.category() );

being used nowadays to avoid the overhead in .clear caused by the "magic 
static" Niall talks about.

This latter "idiom" is obviously broken after NIall's suggested change 
though.

> I'm also not happy to have to convert that initialization to
>
>      err = error_code();
>
> because it loses information about the error category, which may be useful 
> if I want to print `err` to log even if it is a success.

Interesting. You rely on there being different success error_codes? This is 
also in direct opposition to the requested change.

How would you suggest we solve the problem of zero being an error in some 
contexts?