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### 3060. `XXX_scan` algorithms are specified to work with move-only `T`, but are specified to make `N` copies of `T` into the destination range

Section: 27.10.8 [exclusive.scan], 27.10.9 [inclusive.scan], 27.10.10 [transform.exclusive.scan], 27.10.11 [transform.inclusive.scan] Status: New Submitter: Billy O'Neal III Opened: 2018-02-06 Last modified: 2019-01-20

Priority: 2

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Discussion:

All of the scan algorithms ([exclusive.scan], [inclusive.scan], [transform.exclusive.scan], [transform.inclusive.scan]) have language like "If `init` is provided, `T` shall be `MoveConstructible` (Table 23); otherwise, `ForwardIterator1`'s value type shall be `MoveConstructible`.". However, the algorithms operational semantics require that that type be written "by copy" to the destination range, making support for move only types impossible.

We probably need to examine real implementations of these things and see what requirements are actually necessary, as in general `GENERALIZED_SUM` and `GENERALIZED_NONCOMMUTATIVE_SUM` need to specify the type used to store intermediate calculations.

[2019-01-20 Reflector prioritization]

Set Priority to 2

Proposed resolution: