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: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2018-01-12 18:55:57

On 01/12/18 21:46, Peter Dimov via Boost wrote:
> Andrey Semashev wrote:
>> > It will only be broken if you rely on `error_code( 0, some-category 
>> )` > to contextually-convert to `false`.
>>
>> I'm not sure how I can *not* rely on that since I construct 
>> `error_code` from enums or ints, all of them having 0 as the "success" 
>> value precisely to allow the contextual conversion produce the 
>> intended result.
> 
> That's exactly what Niall wanted to know, I suppose; would it be 
> possible for you to give specific examples from your code that would be 
> broken?

I suppose, code like this:

   enum class my_errors
   {
     success = 0
   };

   void foo(error_code& err)
   {
     // Do stuff...
     err = make_error_code(success); // error_code(0, my_category)
   }

   void bar()
   {
     error_code err;
     foo(err);
     if (err)
       complain();
   }

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`. 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.