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4073. concat_view::size may overflow

Section: 25.7.18.2 [range.concat.view] Status: New Submitter: Hewill Kang Opened: 2024-04-21 Last modified: 2024-06-24

Priority: 4

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Discussion:

Currently, concat_view::size returns the sum of sizes of all underlying ranges, and the return type is specified to be the common type of all sizes, which may lead to potential overflow:

auto r = std::views::iota(0uz, SIZE_MAX);
std::print("{}\n", r.size());            // 18446744073709551615 (size_t)
std::print("{}\n", r.end() - r.begin()); // 18446744073709551615 (__int128)

auto c = std::views::concat(r, r);    
std::print("{}\n", c.size());            // 18446744073709551614 (size_t)
std::print("{}\n", c.end() - c.begin()); // 36893488147419103230 (__int128)

[2024-06-24; Reflector poll]

Set priority to 4 after reflector poll. Same behaviour as join_view, was there some discussion of this being covered by general wording?

Proposed resolution: