| use std::mem; |
| use std::mem::MaybeUninit; |
| use std::slice; |
| |
| /// `Vec::spare_capacity_mut` is not stable until Rust 1.60. |
| pub(crate) fn vec_spare_capacity_mut<A>(vec: &mut Vec<A>) -> &mut [MaybeUninit<A>] { |
| // SAFETY: copy-paste from rust stdlib. |
| unsafe { |
| slice::from_raw_parts_mut( |
| vec.as_mut_ptr().add(vec.len()) as *mut MaybeUninit<A>, |
| vec.capacity() - vec.len(), |
| ) |
| } |
| } |
| |
| /// `MaybeUninit::write_slice` is not stable. |
| pub(crate) fn maybe_uninit_write_slice<'a, T>( |
| this: &'a mut [MaybeUninit<T>], |
| src: &[T], |
| ) -> &'a mut [T] |
| where |
| T: Copy, |
| { |
| // SAFETY: copy-paste from rust stdlib. |
| |
| let uninit_src: &[MaybeUninit<T>] = unsafe { mem::transmute(src) }; |
| |
| this.copy_from_slice(uninit_src); |
| |
| unsafe { &mut *(this as *mut [MaybeUninit<T>] as *mut [T]) } |
| } |
| |
| /// `MaybeUninit::array_assume_init` is not stable. |
| #[inline] |
| pub(crate) unsafe fn maybe_ununit_array_assume_init<T, const N: usize>( |
| array: [MaybeUninit<T>; N], |
| ) -> [T; N] { |
| // SAFETY: |
| // * The caller guarantees that all elements of the array are initialized |
| // * `MaybeUninit<T>` and T are guaranteed to have the same layout |
| // * `MaybeUninit` does not drop, so there are no double-frees |
| // And thus the conversion is safe |
| (&array as *const _ as *const [T; N]).read() |
| } |
| |
| /// `MaybeUninit::write` is stable since 1.55. |
| #[inline] |
| pub(crate) fn maybe_uninit_write<T>(uninit: &mut MaybeUninit<T>, val: T) -> &mut T { |
| // SAFETY: copy-paste from rust stdlib. |
| *uninit = MaybeUninit::new(val); |
| unsafe { &mut *uninit.as_mut_ptr() } |
| } |