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What is an access in [res.on.objects]?

From: Eric Schmidt <eric41293_at_[hidden]>
Date: Wed, 19 Oct 2022 19:11:03 -0700
This issue came up on a StackOverflow question:


This led to a discussion here:


Now, https://eel.is/c++draft/res.on.objects states

"If an object of a standard library type is accessed, and the beginning
of the object's lifetime does not happen before the access, or the
access does not happen before the end of the object's lifetime, the
behavior is undefined unless otherwise specified."

According to a non-normative note in https://eel.is/c++draft/defns.access,

"Only glvalues of scalar type can be used to access objects. ...
Attempts to read or modify an object of class type typically invoke a
constructor or assignment operator; such invocations do not themselves
constitute accesses, although they may involve accesses of scalar

The question is, can objects of class type be accessed? Is it the intent
that an access to a scalar subobject also constitutes an access to the
object itself?

If not, then it is impossible for objects of most library types to be
accessed. If so, then objects of many library types are unavoidably
accessed by their own destructor, after the end of their lifetime.
Either way, [res.on.objects] doesn't work.

For reference, here is some previous discussion from 2014:


And the LWG issue that led to the current wording:


Received on 2022-10-20 02:11:39