pub fn pin_in(x: T, alloc: A) -> Pin<Self>
    where
        A: 'static,
    {
        Self::new_in(x, alloc).into()
    }
Constructs a new boxed slice with uninitialized contents in the provided allocator.

# Examples

```
#![feature(allocator_api, new_uninit)]

use std::alloc::System;

let mut values = Box::<[u32], _>::new_uninit_slice_in(3, System);

let values = unsafe {
// Deferred initialization:
benchmarks/haystacks/code/rust-library.rs