diff --git a/alloc/src/boxed.rs b/alloc/src/boxed.rs index f299aa0124dbe..405430377e551 100644 --- a/alloc/src/boxed.rs +++ b/alloc/src/boxed.rs @@ -704,7 +704,7 @@ impl Box<[T]> { } /// Constructs a new boxed slice with uninitialized contents. Returns an error if - /// the allocation fails + /// the allocation fails. /// /// # Examples /// @@ -739,7 +739,7 @@ impl Box<[T]> { } /// Constructs a new boxed slice with uninitialized contents, with the memory - /// being filled with `0` bytes. Returns an error if the allocation fails + /// being filled with `0` bytes. Returns an error if the allocation fails. /// /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and incorrect usage /// of this method. @@ -831,6 +831,85 @@ impl Box<[T], A> { pub fn new_zeroed_slice_in(len: usize, alloc: A) -> Box<[mem::MaybeUninit], A> { unsafe { RawVec::with_capacity_zeroed_in(len, alloc).into_box(len) } } + + /// Constructs a new boxed slice with uninitialized contents in the provided allocator. Returns an error if + /// the allocation fails. + /// + /// # Examples + /// + /// ``` + /// #![feature(allocator_api, new_uninit)] + /// + /// use std::alloc::System; + /// + /// let mut values = Box::<[u32], _>::try_new_uninit_slice_in(3, System)?; + /// let values = unsafe { + /// // Deferred initialization: + /// values[0].as_mut_ptr().write(1); + /// values[1].as_mut_ptr().write(2); + /// values[2].as_mut_ptr().write(3); + /// values.assume_init() + /// }; + /// + /// assert_eq!(*values, [1, 2, 3]); + /// # Ok::<(), std::alloc::AllocError>(()) + /// ``` + #[unstable(feature = "allocator_api", issue = "32838")] + #[inline] + pub fn try_new_uninit_slice_in( + len: usize, + alloc: A, + ) -> Result], A>, AllocError> { + let ptr = if T::IS_ZST || len == 0 { + NonNull::dangling() + } else { + let layout = match Layout::array::>(len) { + Ok(l) => l, + Err(_) => return Err(AllocError), + }; + alloc.allocate(layout)?.cast() + }; + unsafe { Ok(RawVec::from_raw_parts_in(ptr.as_ptr(), len, alloc).into_box(len)) } + } + + /// Constructs a new boxed slice with uninitialized contents in the provided allocator, with the memory + /// being filled with `0` bytes. Returns an error if the allocation fails. + /// + /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and incorrect usage + /// of this method. + /// + /// # Examples + /// + /// ``` + /// #![feature(allocator_api, new_uninit)] + /// + /// use std::alloc::System; + /// + /// let values = Box::<[u32], _>::try_new_zeroed_slice_in(3, System)?; + /// let values = unsafe { values.assume_init() }; + /// + /// assert_eq!(*values, [0, 0, 0]); + /// # Ok::<(), std::alloc::AllocError>(()) + /// ``` + /// + /// [zeroed]: mem::MaybeUninit::zeroed + #[unstable(feature = "allocator_api", issue = "32838")] + #[inline] + pub fn try_new_zeroed_slice_in( + len: usize, + alloc: A, + ) -> Result], A>, AllocError> { + let ptr = if T::IS_ZST || len == 0 { + NonNull::dangling() + } else { + let layout = match Layout::array::>(len) { + Ok(l) => l, + Err(_) => return Err(AllocError), + }; + alloc.allocate_zeroed(layout)?.cast() + }; + unsafe { Ok(RawVec::from_raw_parts_in(ptr.as_ptr(), len, alloc).into_box(len)) } + } } impl Box, A> {