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

Subject: Re: [boost] [variant2] Andrzej's review -- design
From: Gavin Lambert (boost_at_[hidden])
Date: 2019-04-04 22:13:56

On 4/04/2019 13:26, Emil Dotchevski wrote:
> Consistent with the basic guarantee, if you assign one std::vector to
> another and the copy operation fails, the contents of the target vector is
> not specified, but it is guaranteed to be a valid vector, so that if you
> happen to handle it later, you can safely do with it what you do with any
> other vector: you can insert or delete elements, iterate, whatever.
> 
> By analogy with your position, a better design for std::vector would be to
> define a special "error" state that you must check for *every* time you
> handle a vector, and the justification for that design is that otherwise it
> might be unexpected to see a vector in a half-copied (but valid, by
> definition) state. Do you see the practical difference now?

No, because vector already has that state -- it's called "a vector with 
size zero" (aka "empty"), which is the same state it typically 
transitions to when successfully moved-from.

This is also the case for all the smart pointer types.

I am saying that variant should behave exactly the same way.  It's what 
people expect.