Date: Thu, 9 Sep 2021 15:07:14 +0000
> On Sep 8, 2021, at 9:58 PM, Jason McKesson via Std-Proposals <std-proposals_at_lists.isocpp.org> wrote:
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> On Wed, Sep 8, 2021 at 2:29 PM D'Alessandro, Luke K via Std-Proposals
> <std-proposals_at_lists.isocpp.org> wrote:
>> I guess I have two questions:
>> 1. Does std::construct_at change the active member of a union?
> As stated in [class.union]/2, "a non-static data member is active if
> its name refers to an object whose lifetime has begun and has not
> ended." `construct_at` can begin the lifetime of objects (which can
> also cause the lifetime of other overlapping objects to end).
> Therefore, it can change the active union member.
Oh that’s great! Relying on the note seemed like a sketchy proposition.
>> 2. If 1, can std::construct_at benefit from the logic in https://eel.is/c++draft/class.union#general-6 that begins the lifetime of a nominated member?
> No. That paragraph applies to the explicit use of the assignment operator.
Okay, so it’s not really possible to directly interact with the array in the way that I wanted to. Johel Ernesto Guerrero Peña pointed out that I should be able to indirectly start the lifetime of an array for non-assignable types as:
constexpr void f()
s.x = 0; // <-- starts the lifetime of both s.x and s.data
Thank you for the help.
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Received on 2021-09-09 10:09:05