Note scoping differences between *x and *x.deref() , and a[b] and *a.index(b)

[dianne]

The equivalences between the overloaded operator expressions and their associated function call forms don't hold in the presence of temporary lifetime extension; this adjusts the rules accordingly and adds examples.

[dianne]

The sections on field access expressions and tuple indexing expressions may also benefit from similar examples or links to that example, in case it needs clarifying that the way they autoderef is scoped more like repeatedly applying * than repeatedly applying a deref method. The autoderef section on the field access expressions page is in line with that, but doesn't clarify. The tuple indexing expressions section doesn't account for autoderef at all, so it would need to be reworked first.

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[dianne]

@rustbot ready

I'll open a separate PR to add text for Box to the * operator expression documentation.

[ehuss]

When looking at this, we felt that this probably shouldn't be part of a note, but instead should be incorporated into the rule itself. The "is equivalent to" is not entirely true due to this exception. How about just adding this text here:

Suggested change

	For other types an index expression `a[b]` is equivalent to `*std::ops::Index::index(&a, b)`, or `*std::ops::IndexMut::index_mut(&mut a, b)` in a mutable place expression context.
	For other types an index expression `a[b]` is equivalent to `*std::ops::Index::index(&a, b)`, or `*std::ops::IndexMut::index_mut(&mut a, b)` in a mutable place expression context, except that when the index expression undergoes [temporary lifetime extension], the indexed expression `a` also has its temporary lifetime extended.

and then include the rust example as you have.

[dianne]

Seems good to me! I couldn't figure out a way to keep the link to destructors.scope.lifetime-extension.sub-expressions without it getting overly cluttered, but maybe it's fine to leave it out?

[rustbot]

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.