4157. The resolution of LWG3465 was damaged by P2167R3

Section: 17.11.6 [cmp.alg] Status: Tentatively Ready Submitter: Jiang An Opened: 2024-09-18 Last modified: 2024-10-02

Priority: Not Prioritized

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Discussion:

In the resolution of LWG 3465, F < E was required to be well-formed and implicitly convertible to bool. However, P2167R3 replaced the convertibility requirements with just "each of decltype(E == F) and decltype(E < F) models boolean-testable", which rendered the type of F < E underconstrained.

[2024-10-02; Reflector poll]

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

Proposed resolution:

This wording is relative to N4988.

1. Modify 17.11.6 [cmp.alg] as indicated:

   (6.3) — Otherwise, if the expressions E == F, E < F, and F < E are all well-formed and each of decltype(E == F) and, decltype(E < F) , and decltype(F < E) models boolean-testable,

   
     E == F ? partial_ordering::equivalent :
     E < F  ? partial_ordering::less :
     F < E  ? partial_ordering::greater :
              partial_ordering::unordered
   

   except that E and F are evaluated only once.