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### 3628. "Effects: Equivalent to:" and uninitialized memory algorithms

Section: 27.11 [specialized.algorithms] Status: New Submitter: Jiang An Opened: 2021-10-23 Last modified: 2022-01-29

Priority: 3

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Discussion:

Most uninitialized memory algorithms (27.11 [specialized.algorithms]) are specified by plain "Effects: Equivalent to:". According to 16.3.2.4 [structure.specifications]/4, such wording requires propagation of "Constraints" of selected constructors. The first two overloads of `std::reduce` (27.10.4 [reduce]) are specified similarly.

I feel the wording for uninitialized memory algorithms is incorrect, because it means that the constraints, especially for algorithms in the `std`, depend on "`Constraints`" in the specifications of many standard library types (but not any user-defined type), which is implementable but brings serious inconsistency.

Perhaps we should add "Mandates:" to these algorithms (except for algorithms in `std::ranges`).

[2022-01-29; Reflector poll]

Set priority to 3 after reflector poll.
Tim: "P2. Not for this particular case (I'm pretty sure there'll be agreement that this shouldn't induce any constraint), but for the more general issue of "Effects: Equivalent to" propagating Constraints:; I'm not sure that's the right approach in general (unlike the other elements, Constraints: requires special handling beyond "use this code" and is pretty hard to work through if we have a lengthy code block) - and it certainly doesn't really make a lot of sense to propagate Constraints: but not actual core-language constraints."

Proposed resolution: