[PATH][_GLIBCXX_DEBUG] Fix unordered container merge

[François Dumont]

On 21/10/21 6:55 pm, Jonathan Wakely wrote:
>
>
> On Thu, 21 Oct 2021 at 17:52, François Dumont <frs.dumont@gmail.com 
> <mailto:frs.dumont@gmail.com>> wrote:
>
>     I eventually would like to propose a different approach.
>
>     I am adding a hook in normal implementation to let the
>     _GLIBCXX_DEBUG code know when a node is being extracted. This way
>     invalidation is only done by comparing nodes, no need to compute
>     hash code for this operation.
>
>
> Ugh, this is horrible, I don't like the normal mode depending on the 
> debug mode (even if it's just having to add hooks like this).

Yes, I was relunctant to do so but in this case I was not able to find 
another way to provide the same result as here.

Ok, I'll come back to the other patch and just invalidate all iterators 
in case of exception.

>
> The previous patch seemed fine to me. Already an improvement on what 
> is on trunk now.
>