"9. Implementing Vec": Dangling pointer overflow?

[kuzminrobin]

I have an impression that in section 9.11. Final Code any fragment containing usize) + or usize + can overflow usize (equal to a dangling pointer), which will result in a panic in debug mode.

See also fragment of interest:

RawVec {
    ptr: NonNull::dangling(),

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Details. The vector's buffer pointer is initialized to a dangling pointer value (so potentially the dangling buffer pointer can be close to overflowing).

For the zero-sized types the buffer is never allocated (the grow() is never called). So the buffer pointer stays dangling.

During the iterator creation the iterator's pointer RawValIter::end is initialized to the value ((slice.as_ptr() as usize) + slice.len()), where the fragment as usize) + can overflow the usize (equal to a dangling pointer); also the iterator's pointer RawValIter::start is initialized to the dangling pointer value (possibly close to overflowing), and during subsequent next() the fragment self.start as usize + 1 can overflow the usize.

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Would be nice to see in the text of the book (e.g. in 9.11. Final Code)

• either the confirmation that the overflow can happen (and the reader should handle accordingly),
• or the explanation why the overflow cannot happen.