4181. Some ranges have negative ssize

Section: 24.7 [iterator.range], 25.3.11 [range.prim.ssize] Status: New Submitter: Casey Carter Opened: 2024-12-13 Last modified: 2025-02-07

Priority: 3

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Discussion:

There exist range types R whose size is representable by neither ptrdiff_t nor make-signed-like-t<ranges::range_size_t<R>>, specifically views::iota(size_t(0), size_t(-1)). It's unfortunate that std::ssize and ranges::ssize produce a negative size for such ranges even when their difference type is capable of representing their size (see demo). Perhaps the ssize overloads should return static_cast<common_type_t<ptrdiff_t, iter_difference_t<decltype(meow.begin())>>>(meow.size()) instead when the argument meow models range?

[2025-02-07; Reflector poll]

Set priority to 3 after reflector poll.

"The behaviour for Ranges regressed due to LWG 3403. It might have been a mistake to broaden the domain of ranges::ssize to match that of ranges::size. The latter includes some non-Range arguments to ease the transition from std::size, but thjere was no existing body of pre-C++20 code calling std::ssize that needed a transition path."

Proposed resolution: