Constification of BinaryHeap construction

[terrarier2111]

Is there any reason this isn't const yet? This should only depend on vec's construction being const which it is.

[est31]

All the other collections already have const constructors (except for the ones for which it's hard, cc #112354). So I think it makes a lot of sense to make this const as well.

There was an entire ACP for VecDequeue::new(). I don't know if one is needed for BinaryHeap as well. On the other hand, the function became instantly const-stable, there was no period where it was unstably const, see #105072.

[tsemo4917]

impl<T: Ord> BinaryHeap<T> {
    pub fn new() -> BinaryHeap<T> {
        BinaryHeap { data: vec![] }
    }
}

BinaryHeap constructor is only depends on Vec constructor, and Vec::new() has been a const function since 1.39.0.

Constification of BinaryHeap constructor will be helpful when a static variable is of the BinaryHeap type.

@dtolnay

[dtolnay]

Please send a PR.

[Coekjan]

I also met this issue and I am trying to address it with #117316

[Coekjan]

The feature const_binary_heap_constructor was added to nightly.

Due to the unstable feature (allocator_api, issue: #32838 ), this feature is not able to be stablized now.