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### 3064. How do uninitialized memory algorithms obtain pointer without undefined behavior?

Section: 27.11 [specialized.algorithms] Status: New Submitter: Alisdair Meredith Opened: 2018-02-12 Last modified: 2020-05-02

Priority: 3

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Discussion:

A typical specification of the algorithms for initializing raw memory in `<memory>` looks like:

> Effects: Equivalent to:

> >     for (; first != last; ++first)
> >       ::new (static_cast<void*>(addressof(*first)))
> >         typename iterator_traits<ForwardIterator>::value_type;

However, this hides a nasty question:

How do we bind a reference to an uninitialized object when dereferencing our iterator, so that `static_cast<void*>(addressof(*first))` does not trigger undefined behavior on the call to `*first`?

When pointers are the only iterators we cared about, we could simply cast the iterator value to `void*` without dereferencing. I don't see how to implement this spec safely without introducing another customization point for iterators that performs the same function as casting a pointer to `void*` in order to get the address of the element.

[2018-02-20, Priority set to 3 after mailing list discussion]

Proposed resolution: