On Tue, Mar 4, 2025 at 3:03 PM Zhihao Yuan <zy_at_[hidden]> wrote:

> On Tuesday, March 4th, 2025 at 9:44 AM, Arthur O'Dwyer via Std-Proposals <
> std-proposals_at_[hidden]> wrote:
>
> On Tue, Mar 4, 2025 at 10:01 AM Avi Kivity via Std-Proposals <
> std-proposals_at_[hidden]> wrote:
>
>> C++ has a literal range type: std::initializer_list. However, its
>> elements are const and so initializing a container from the elements
>> involves a copy.
>>
>> [...] A suitable proposal in this area should be able to compile
> std::vector<std::unique_ptr<int>> v = { std::make_unique<int>(1),
> std::make_unique<int>(2) };
> right out of the box. If we aren't enabling people to write *that*, then
> we aren't really helping them.
>
>
> If someone is designing their own container,
> a simple rvalue reference to array is usually
> enough
>
> template<size_t N>
> vector(T (&&arr)[N]);
>
> // use
> vector v1({2, 4});
> vector v2({std::make_unique<int>(1), std::make_unique<int>(2)});
>
> https://godbolt.org/z/4fbYc37n6
>

I would be skeptical of that, though.
(1) That disables the "normal" way of constructing from a bag of elements:
    vector v1 = {2, 4}; // no longer works
(2) That disables P2752 static-storage optimization:
https://godbolt.org/z/sTnqqaove
    vector v1({
      #embed "large-file.dat" // compiles, but blows your stack at runtime
    });

Admittedly both of these might be classified as mere hobbyhorses of *mine*,
that nobody else cares about. In fact I recall you had opinions of some
kind about applying P2752 to array literals too, which I shot down as scope
creep; do you think it's *possible* to fix the codegen in #2 with a
core-language change? The problem I see is that you're explicitly *wanting*
to move-out-of the elements of `arr`, so it can't possibly go into static
storage, right?

–Arthur

>