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3063. Parallel algorithms in <memory> are underspecified

Section: 19.10.11 [specialized.algorithms] Status: New Submitter: Alisdair Meredith Opened: 2018-02-12 Last modified: 2018-03-03

Priority: 3

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The parallel forms of the uninitialized memory algorithms in <memory> are underspecified in two ways. First, they missed the change that all parallel algorithms require at least Forward Iterators, even for input ranges. See P0467R2 for more details.

The second problem is that they do not have a separate specification to the serial forms. This is a problem in two ways. First, there is no more blanket wording saying a parallel policy algorithm has the same semantics as the serial form unless otherwise specified, so in principle these algorithms are totally unspecified. However, assuming that intent, all of the existing specifications use an as-if formulation with code that is explicitly serial in nature, so need a new specification that talks about the effects on each element without including the iteration order.

[2018-02-20, Priority set to 3 after mailing list discussion]

Proposed resolution: