Issue 3948: possibly-const-range and as-const-pointer should be noexcept (original) (raw)

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3948. _possibly-const-range_ and _as-const-pointer_ should be noexcept

Section: 25.2 [ranges.syn], 25.3.16 [range.prim.cdata] Status: WP Submitter: Jiang An Opened: 2023-06-20 Last modified: 2023-11-22

Priority: Not Prioritized

View all other issues in [ranges.syn].

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Discussion:

As of P2278R4, several range access CPOs are specified with _possibly-const-range_and _as-const-pointer_. These helper functions never throw exceptions, but are not marked with noexcept. As a result, implementations are currently allowed to make a call to ranges::c_cpo_ potentially throwing while the underlying ranges::_cpo_ call is non-throwing, which doesn't seem to be intended.

[2023-10-27; Reflector poll]

Set status to Tentatively Ready after five votes in favour during reflector poll.

[2023-11-11 Approved at November 2023 meeting in Kona. Status changed: Voting → WP.]

Proposed resolution:

This wording is relative to N4950.

1. Modify 25.2 [ranges.syn], header <ranges> synopsis, as indicated:

   […]
   // 25.7.22 [range.as.const], as const view
   template
   constexpr auto& possibly-const-range(R& r) noexcept { // exposition only
   if constexpr (constant_range && !constant_range) {
   return const_cast<const R&>(r);

} else {
return r;
}
}
[…] 2. Modify 25.3.16 [range.prim.cdata] before p1 as indicated:
template
constexpr auto as-const-pointer(const T* p) noexcept { return p; } // exposition only