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3022. is_convertible<derived*, base*> may lead to ODR

Section: 21.3.7 [meta.rel] Status: Resolved Submitter: Alisdair Meredith Opened: 2017-09-24 Last modified: 2018-11-12

Priority: 2

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Discussion:

Given two incomplete types, base and derived, that will have the expected base/derived relationship when complete, the trait is_convertible claims to support instantiation with pointers to these types (as pointers to incomplete types are, themselves, complete), yet will give a different answer when the types are complete vs. when they are incomplete.

We should require pointers (and pointers to pointers etc.) point to a complete type, unless one is a pointer to cv-void. We may also want some weasel-wording to permit pointers to arrays-of-unknown-bound, and pointers to cv-qualified variants of the same incomplete type.

[2017-11 Albuquerque Wednesday night issues processing]

Priority set to 2

[2018-08 Batavia Monday issue discussion]

Issues 2797⁽ⁱ⁾, 2939⁽ⁱ⁾, 3022⁽ⁱ⁾, and 3099⁽ⁱ⁾ are all closely related. Walter to write a paper resolving them.

[2018-11-11 Resolved by P1285R0, adopted in San Diego.]

Proposed resolution: