P3698 R0 Cross-capacity comparisons for inplace_vector

[wg21bot]

P3698R0 Cross-capacity comparisons for inplace_vector (Charles Hussong)

[inbal2l]

2025-06-03 Library Evolution Telecon

P3698R0: Cross-capacity comparisons for inplace_vector

2025-06-03 Library Evolution Telecon Minutes

Champion: Charles Hussong
Chair: Inbal Levi
Minute Taker: Bronek Kozicki

Summary

POLL: We would like to have the example presented in line 1 P3698R0 to return true:

#include
#include

int main() {
std::inplace_vector<int, 10> x{1, 2, 3};
std::inplace_vector<int, 100> y{1, 2, 3};
assert(x == y); // 1 Now: compilation error: decltype(x) not comparable with decltype(y), with paper: true
}

SF	F	N	A	SA
7	6	3	4	2

Attendance: 24
Author's Position: F
Outcome: Weak consensus in favor

A: The actual implementation does not affect my opinion - the paper is missing motivation why this should work.
A: I am bit concerned about inconsistency with array, I would like to see some discussion on consistency.

Next Steps

There was a weak consensus for encoregment for making this change in behaviour.
A few options came up in regards to the best technical solution for modifying the overload set (hidden friend/free function/constraited/templated on the capacity/etc.)
Please send your favorite solution to the author before Sofia on mail - they will make sure he captures all these options (and with working examples) in the paper, including impact of different shipping vehicles.
The paper will be seen again during Sofia.