Hi all,
Recently I noticed item #10 in section 14.4 (Handling an exception), n4917.pdf
(https://github.com/cplusplus/draft/releases/latest):
10 Referring to any non-static member or base class of an object in the
handler for a function-try-block of a constructor or destructor for
that object results in undefined behavior.
Unfortunately, that item isn't elaborated, and somehow I find it
puzzling. Cleary, if a class has composed data members then the destructors of
those already constructed data members have been called when the execution
reaches the constructor's function-try-block handler.
This seems to me a simple corollary of [class.cdtor], particularly paragraph 1. I'd even question whether normative wording is necessary under [except.handle]; this could probably be a note.
But why would referring to members of basic data types like 'int' be
undefined?
If the data member is a member of a virtual base class, the vtable (speaking concretely) and the offsets it contains necessary to compute the address of that member may no longer be valid.
There is an issue that [class.cdtor] is actually more restrictive here than [basic.life], meaning that operations that are allowed on an object fully outside its lifetime (principally, referring to a non-virtual base class) can no longer be performed once it is under construction or destruction. I'm not sure if we've got around to opening a CWG issue there.