Re: [boost] [variant2] Andrzej's review -- design

Subject: Re: [boost] [variant2] Andrzej's review -- design
From: Larry Evans (cppljevans_at_[hidden])
Date: 2019-04-06 02:55:21

On 4/5/19 7:46 PM, Emil Dotchevski via Boost wrote:
> On Thu, Apr 4, 2019 at 4:30 PM Gavin Lambert via Boost <
> boost_at_[hidden]> wrote:
>> The problem with transitioning to an otherwise valid but unexpected
>> state is that it may end up evaluating unintended code
> 
> This is why I made the analogy with std::vector. Let's say you always put
> exactly 10 elements in all your vectors, but then you assign one vector to
> another, and that fails, and now (unexpectedly?) you have an (otherwise
> valid) vector with fewer than 10 elements.
> 
> Such is life. This is how the basic guarantee works, you get an unspecified
> but valid state.
> 
>> (Granted, continuing evaluation on a faulted variable is already a bug
>> in itself, but you are making detection of that bug harder by not
>> putting the value into an obviously-faulted state.)
> 
> I do not think that it is a bug to access an object that is in a valid
> state. In fact, the reason why the state is defined as valid is so that you
> can safely work with that object, even after a failure was reported.

I'm guessing "unexpected" could mean the std::vector
could have some arbitrary number of elements all filled with random
values.  I don't see how you can do anything useful with that.