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### 3333. `ranges::cbegin/ranges::cend`, (and maybe `ranges::crbegin/ranges::crend`) are under-specified to allow rvalue-arrays

Section: 24.3.4 [range.access.cbegin], 24.3.5 [range.access.cend] Status: NAD Submitter: Christopher Di Bella Opened: 2019-11-06 Last modified: 2020-02-13

Priority: Not Prioritized

View all issues with NAD status.

Discussion:

The following should be ill-formed, but is not, likely due to decay-to-pointer or reference collapsing.

>     double x[321];
>     ranges::cbegin(std::move(x)); // should be ill-formed
>     ranges::cend(std::move(x));   // should be ill-formed

This might be a problem for `ranges::crbegin` and `ranges::crend`, but I haven't implemented any of `rbegin`, `rend`, `crbegin`, and `crend` to confirm as much.

[2020-02 Status to NAD on Thursday morning in Prague.]

Proposed resolution:

This wording is relative to N4835.

1. Change 24.3.4 [range.access.cbegin] as indicated:

   > -1- The name `ranges::cbegin` denotes a customization point object (16.3.3.3.6 [customization.point.object]). If t The expression `ranges::cbegin(E)` for some subexpression `E` of type `T` is well-formed, then the expression `ranges::cbegin(E)` is expression-equivalent to:

   > 1. (1.1) — `ranges::begin(static_cast<const T&>(E))` if `E` is an lvalue.

   > 2. (1.2) — Otherwise, `ranges::begin(static_cast<const T&&>(E))`.

2. Change 24.3.5 [range.access.cend] as indicated:

   > -1- The name `ranges::cend` denotes a customization point object (16.3.3.3.6 [customization.point.object]). If t The expression `ranges::cend(E)` for some subexpression `E` of type `T` is well-formed, then the expression `ranges::cend(E)` is expression-equivalent to:

   > 1. (1.1) — `ranges::end(static_cast<const T&>(E))` if `E` is an lvalue.

   > 2. (1.2) — Otherwise, `ranges::end(static_cast<const T&&>(E))`.