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Loosen From<&[T]> for Box<[T]> bound to T: Clone #103406

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merged 2 commits into from
Apr 30, 2023
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Loosen From<&[T]> for Box<[T]> bound to T: Clone #103406

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075ee26
Loosen `From<&[T]> for Box<[T]>` bound to T: Clone
Jules-Bertholet Oct 22, 2022
18d2c60
`cfg`-gate `BoxFromSlice` trait
Jules-Bertholet Apr 29, 2023
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39 changes: 31 additions & 8 deletions library/alloc/src/boxed.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1455,9 +1455,36 @@ where
}
}

/// Specialization trait used for `From<&[T]>`.
#[cfg(not(no_global_oom_handling))]
trait BoxFromSlice<T> {
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fn from_slice(slice: &[T]) -> Self;
}

#[cfg(not(no_global_oom_handling))]
impl<T: Clone> BoxFromSlice<T> for Box<[T]> {
#[inline]
default fn from_slice(slice: &[T]) -> Self {
slice.to_vec().into_boxed_slice()
}
}

#[cfg(not(no_global_oom_handling))]
impl<T: Copy> BoxFromSlice<T> for Box<[T]> {
#[inline]
fn from_slice(slice: &[T]) -> Self {
let len = slice.len();
let buf = RawVec::with_capacity(len);
unsafe {
ptr::copy_nonoverlapping(slice.as_ptr(), buf.ptr(), len);
buf.into_box(slice.len()).assume_init()
}
}
}

#[cfg(not(no_global_oom_handling))]
#[stable(feature = "box_from_slice", since = "1.17.0")]
impl<T: Copy> From<&[T]> for Box<[T]> {
impl<T: Clone> From<&[T]> for Box<[T]> {
/// Converts a `&[T]` into a `Box<[T]>`
///
/// This conversion allocates on the heap
Expand All @@ -1471,19 +1498,15 @@ impl<T: Copy> From<&[T]> for Box<[T]> {
///
/// println!("{boxed_slice:?}");
/// ```
#[inline]
fn from(slice: &[T]) -> Box<[T]> {
let len = slice.len();
let buf = RawVec::with_capacity(len);
unsafe {
ptr::copy_nonoverlapping(slice.as_ptr(), buf.ptr(), len);
buf.into_box(slice.len()).assume_init()
}
<Self as BoxFromSlice<T>>::from_slice(slice)
}
}

#[cfg(not(no_global_oom_handling))]
#[stable(feature = "box_from_cow", since = "1.45.0")]
impl<T: Copy> From<Cow<'_, [T]>> for Box<[T]> {
impl<T: Clone> From<Cow<'_, [T]>> for Box<[T]> {
/// Converts a `Cow<'_, [T]>` into a `Box<[T]>`
///
/// When `cow` is the `Cow::Borrowed` variant, this
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