However thanks for explaining the issue. This one is obvious and I just completely failed to think about how you ensure the source object is in a safe state if an exception occurs part way through moving the source data. It seems to imply the old MSVC behaviour was incorrect in such a scenario, but I hadn’t considered that possibility so assumed it was correct and therefore didn’t think of why this behaviour is required.

My solution is of course to simply not allow exceptions because the c++ model of everything implicitly throwing is just as annoying as Java’s “let’s explicitly annotate everything” model albeit with different paths to sadness.