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Commit1632165

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Rollup merge ofrust-lang#125995 - kpreid:const-uninit-stable, r=Nilstrieb
Use inline const blocks to create arrays of `MaybeUninit`.This PR contains 2 changes enabled by the fact that [`inline_const` is now stable](rust-lang#104087), and was split out ofrust-lang#125082.1. Use inline const instead of `unsafe` to construct arrays in `MaybeUninit` examples. Rationale: Demonstrate good practice of avoiding `unsafe` code where it is not strictly necessary.4. Use inline const instead of `unsafe` to implement `MaybeUninit::uninit_array()`. This is arguably giving the compiler more work to do, in exchange for eliminating just one single internal unsafe block, so it's less certain that this is good on net.r​? `@Nilstrieb`
2 parents2c5f1ac +14a6f29 commit1632165

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‎core/src/mem/maybe_uninit.rs‎

Lines changed: 5 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -120,12 +120,8 @@ use crate::slice;
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/// use std::mem::{self, MaybeUninit};
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///
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/// let data = {
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/// // Create an uninitialized array of `MaybeUninit`. The `assume_init` is
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/// // safe because the type we are claiming to have initialized here is a
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/// // bunch of `MaybeUninit`s, which do not require initialization.
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/// let mut data: [MaybeUninit<Vec<u32>>; 1000] = unsafe {
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/// MaybeUninit::uninit().assume_init()
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/// };
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/// // Create an uninitialized array of `MaybeUninit`.
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/// let mut data: [MaybeUninit<Vec<u32>>; 1000] = [const { MaybeUninit::uninit() }; 1000];
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///
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/// // Dropping a `MaybeUninit` does nothing, so if there is a panic during this loop,
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/// // we have a memory leak, but there is no memory safety issue.
@@ -147,10 +143,8 @@ use crate::slice;
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/// ```
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/// use std::mem::MaybeUninit;
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///
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/// // Create an uninitialized array of `MaybeUninit`. The `assume_init` is
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/// // safe because the type we are claiming to have initialized here is a
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/// // bunch of `MaybeUninit`s, which do not require initialization.
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/// let mut data: [MaybeUninit<String>; 1000] = unsafe { MaybeUninit::uninit().assume_init() };
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/// // Create an uninitialized array of `MaybeUninit`.
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/// let mut data: [MaybeUninit<String>; 1000] = [const { MaybeUninit::uninit() }; 1000];
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/// // Count the number of elements we have assigned.
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/// let mut data_len: usize = 0;
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///
@@ -348,8 +342,7 @@ impl<T> MaybeUninit<T> {
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#[must_use]
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#[inline(always)]
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pubconstfnuninit_array<constN:usize>() ->[Self;N]{
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// SAFETY: An uninitialized `[MaybeUninit<_>; LEN]` is valid.
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unsafe{MaybeUninit::<[MaybeUninit<T>;N]>::uninit().assume_init()}
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[const{MaybeUninit::uninit()};N]
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}
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/// Creates a new `MaybeUninit<T>` in an uninitialized state, with the memory being

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