Class destructors - clarify what is safe

[Paul Backus]

On Saturday, 14 February 2026 at 18:42:21 UTC, H. S. Teoh wrote:
>> As we can explicitly call destroy() on a class instance 
>> multiple times, do we need to be "careful" of only closing a 
>> file once, rather than closing a file multiple times, if that 
>> can cause issues.
>
> Calling .destroy on a class object more than once may trigger 
> UB.

This is technically true, in the sense that calling any function 
could conceivably trigger UB, but destructors *should* be 
idempotent, and any destructor marked as @safe *must* be 
idempotent.