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Re: Easier make_unique with deleter function

From: Peter Sommerlad (C++) <"Peter>
Date: Tue, 24 Aug 2021 09:21:50 +0200
Dear Lénárd

thank you for proposing that change in P2413 that I had an itch myself
to propose since I learned that the original motivation for concepts
(~2004) had exactly that example in mind.

I would even consider to argue it is a bug-fix to be applied back to
earlier C++ versions, but that might be too much to ask WG21 for.

If you need a sponsor for P2413, count me in!


Lénárd Szolnoki via Std-Proposals wrote on 24.08.21 08:46:
> Hi,
> With P2413 `std::unique_ptr<Base> base_ptr =
> std::make_unique<Derived>()` would become safer, it would fail to
> compile if Base didn't have a virtual destructor.
> In the recent mailing list review making `std::unique_ptr<Base>
> base_ptr(new Derived());` safer also came up, but it's not proposed
> currently. I don't have a satisfactory solution to make the raw pointer
> constructors safer this way.
> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2413r0.html
> Cheers,
> Lénárd
> ------------------------------------------------------------------------
> *From:* Ville Voutilainen via Std-Proposals <std-proposals_at_[hidden]>
> *Sent:* August 24, 2021 12:38:51 AM GMT+01:00
> *To:* sotrdg sotrdg via Std-Proposals <std-proposals_at_[hidden]>
> *Cc:* Ville Voutilainen <ville.voutilainen_at_[hidden]>
> *Subject:* Re: [std-proposals] Easier make_unique with deleter function
> On Tue, 24 Aug 2021 at 02:22, Jason McKesson via Std-Proposals
> <std-proposals_at_[hidden]> wrote:
> `make_unique` was not added because it was shorter to type. In a
> pre-C++17 world, you couldn't guarantee that two argument expressions
> in the same function call would not interleave with one another. As
> such, `make_unique<T>(Args)` was a more exception-safe version of
> `unique_ptr<T>(Args)`.
> Of course, since C++17 fixed the problem at the language level (the
> argument expressions can happen in any order, but the sub-expressions
> cannot be interleaved), it has become unnecessary.
> It has uses that some audiences consider more important than anything
> else, such as being
> able to avoid using new-expressions to create objects with unique ownership.
> --
> Std-Proposals mailing list
> Std-Proposals_at_[hidden]
> https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals

Peter Sommerlad
Better Software: Consulting, Training, Reviews
Modern, Safe & Agile C++
+41 79 432 23 32

Received on 2021-08-24 02:21:58