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Re: item_traits: A simple solution for destructive move

From: Richard Hodges <hodges.r_at_[hidden]>
Date: Mon, 3 May 2021 11:57:24 +0200
On Mon, 3 May 2021 at 11:22, Rick de Water via Std-Proposals <
std-proposals_at_[hidden]> wrote:

> When working on a container library I needed to manage the complexity of
> moving items around (memcpy when trivial, noexcept or not, copy if not
> movable, etc), and I came up with a traits class that manages everything
> for you. You give it a destination pointer, and often a source pointer, and
> the traits class will do the rest.
> This is already very useful to have, but then I realized that it could
> also easily do a destructive move. By specializing the traits class for a
> destructively movable item (like unique_ptr) it can optimally move the
> items from the source to the destination memory. All container classes can
> then simply use item_traits to move items around whenever needed.
> Here is a simplification of my current implementation:
> template <typename Item>
> struct item_traits
> {
> using value_type = Item;
> using pointer = value_type*;
> using const_pointer = const value_type*;
> using size_type = std::size_t;
> static void construct(pointer destination, size_type size);
> static void destruct(pointer destination, size_type size);
> static void copy(pointer destination, const_pointer source, size_type
> size);
> static void move(pointer destination, pointer source, size_type size);
> static void destructive_move(pointer destination, pointer source,
> size_type size);
> };
> It would of course have a non specialized version that works for all types
> and uses type_traits to determine the optimal way to move things around,
> and destructive_move would simply call move + destruct.

What does it do if the value_type is not copyable?

> Are there any major issues with this idea that would prevent it from
> standardization?

A motivating use case, a paper and a demonstration of it providing
real-world benefit might make it more convincing.

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Received on 2021-05-03 04:57:37