Re: Mother of all Variants

From: Alexander Grund (alexander.grund_at_[hidden])
Date: 2019-06-27 08:00:26

Am 27.06.19 um 09:33 schrieb Gavin Lambert via Boost:
> On 27/06/2019 19:06, degski wrote:
>> Â  Yes, but std::swap must also not invalidate any references, 
>> pointers, or
>> iterators referring to the elements of the containers being swapped, 
>> which
>> leaves the scope for throwing rather small [if at all possible].
>
> Are you sure about that?
>
> Perhaps it is a failure of my imagination (or I'm misunderstanding 
> what you're saying), but that doesn't even seem possible.

On how this is possible: Imagine `std::list` as a simple linked list 
(pointer to (element, pointer-to-next)-tuples).
On move, you simply move the HEAD pointer to the new list and a NULL to 
the old list.

Result: Pointers/References to all elements are still valid. Same for 
e.g. vectors: Only pointers to array are swapped -> Unchanged element 
pointers

obviously after `swap(foo, bar)` an old pointer `oldFoo = &foo[1]` set 
before the swap does now point into `bar`: `assert(oldFoo == &bar[1])`