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4427. meta::dealias needs to work with things that aren't entities

Section: 21.4.7 [meta.reflection.queries] Status: WP Submitter: Jonathan Wakely Opened: 2025-10-24 Last modified: 2025-11-11

Priority: Not Prioritized

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Discussion:

Addresses US 99-205

Several uses of dealias assume that it can be used with reflections that represent direct base class relationships, which are not entities. The spec for dealias says that such uses should fail with an exception.

In the 2025-10-24 LWG telecon it was agreed that dealias should just be the identity function for non-entities.

[Kona 2025-11-03; approved by LWG. Status changed: New → Immediate.]

[Kona 2025-11-08; Status changed: Immediate → WP.]

Proposed resolution:

This wording is relative to N5014.

  1. Modify 21.4.7 [meta.reflection.queries] as indicated:

    consteval info dealias(info r);

    -49- Returns: If r represents an entity, then a A reflection representing the underlying entity of what r represents. Otherwise, r.

    [Example 5:
    ...
    — end example]

    -50- Throws: meta::exception unless r represents an entity.