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4288. The Constraints: element in [time.clock.system.members] is probably wrong

Section: 30.7.2.2 [time.clock.system.members] Status: New Submitter: Jiang An Opened: 2025-06-19 Last modified: 2025-07-15

Priority: Not Prioritized

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Discussion:

Currently, the Constraints: element in 30.7.2.2 [time.clock.system.members] for the member typedef system_clock::rep imposes a requirement for the implementation, without establishing any condition for user code. Perhaps it's wrong to use a Constraints: element there.

Previous resolution [SUPERSEDED]:

This wording is relative to N5008.

1. Modify 30.7.2.2 [time.clock.system.members] as indicated:

   using system_clock::rep = unspecified;
   

   -1- Constraints:The implementation shall ensure that system_clock::duration::min() < system_clock::duration::zero() is true. [Note 1: This implies that rep is a signed type. — end note]

[2025-07-15; Reflector discussion]

The discussion revealed a preference to not insert the additional "The implementation shall ensure that", because its not really needed, since this is just a normal implementation requirement that falls out of the specification.

Proposed resolution:

This wording is relative to N5008.

1. Modify 30.7.2.2 [time.clock.system.members] as indicated:

   using system_clock::rep = unspecified;
   

   -1- Constraints: system_clock::duration::min() < system_clock::duration::zero() is true. [Note 1: This implies that rep is a signed type. — end note]