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alloc: make Cow From impls const #146067

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alloc: make Cow From impls const #146067

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6 changes: 4 additions & 2 deletions library/alloc/src/bstr.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -245,7 +245,8 @@ impl<'a> From<&'a ByteStr> for ByteString {
}

#[unstable(feature = "bstr", issue = "134915")]
impl<'a> From<ByteString> for Cow<'a, ByteStr> {
#[rustc_const_unstable(feature = "const_from", issue = "143773")]
impl<'a> const From<ByteString> for Cow<'a, ByteStr> {
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Do we have the equivalent for String? And is ByteString const constructible

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@oli-obk Yes, the equivalent for String is in this same patch.

ByteString is const constructible:

#[repr(transparent)]
pub struct ByteString(pub Vec<u8>);

Both Vec and String are const constructible:

https://doc.rust-lang.org/std/vec/struct.Vec.html#method.new
https://doc.rust-lang.org/std/string/struct.String.html#method.new

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Oh lol i stopped scrolling and didnt see the other files

#[inline]
fn from(s: ByteString) -> Self {
Cow::Owned(s)
Expand Down Expand Up @@ -598,7 +599,8 @@ impl Clone for Box<ByteStr> {
}

#[unstable(feature = "bstr", issue = "134915")]
impl<'a> From<&'a ByteStr> for Cow<'a, ByteStr> {
#[rustc_const_unstable(feature = "const_from", issue = "143773")]
impl<'a> const From<&'a ByteStr> for Cow<'a, ByteStr> {
#[inline]
fn from(s: &'a ByteStr) -> Self {
Cow::Borrowed(s)
Expand Down
6 changes: 4 additions & 2 deletions library/alloc/src/ffi/c_str.rs
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Expand Up @@ -869,7 +869,8 @@ impl From<CString> for Box<CStr> {
}

#[stable(feature = "cow_from_cstr", since = "1.28.0")]
impl<'a> From<CString> for Cow<'a, CStr> {
#[rustc_const_unstable(feature = "const_from", issue = "143773")]
impl<'a> const From<CString> for Cow<'a, CStr> {
/// Converts a [`CString`] into an owned [`Cow`] without copying or allocating.
#[inline]
fn from(s: CString) -> Cow<'a, CStr> {
Expand All @@ -878,7 +879,8 @@ impl<'a> From<CString> for Cow<'a, CStr> {
}

#[stable(feature = "cow_from_cstr", since = "1.28.0")]
impl<'a> From<&'a CStr> for Cow<'a, CStr> {
#[rustc_const_unstable(feature = "const_from", issue = "143773")]
impl<'a> const From<&'a CStr> for Cow<'a, CStr> {
/// Converts a [`CStr`] into a borrowed [`Cow`] without copying or allocating.
#[inline]
fn from(s: &'a CStr) -> Cow<'a, CStr> {
Expand Down
1 change: 1 addition & 0 deletions library/alloc/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -109,6 +109,7 @@
#![feature(coerce_unsized)]
#![feature(const_default)]
#![feature(const_eval_select)]
#![feature(const_from)]
#![feature(const_heap)]
#![feature(const_trait_impl)]
#![feature(core_intrinsics)]
Expand Down
9 changes: 6 additions & 3 deletions library/alloc/src/string.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3109,7 +3109,8 @@ impl<'a> From<Cow<'a, str>> for String {

#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
impl<'a> From<&'a str> for Cow<'a, str> {
#[rustc_const_unstable(feature = "const_from", issue = "143773")]
impl<'a> const From<&'a str> for Cow<'a, str> {
/// Converts a string slice into a [`Borrowed`] variant.
/// No heap allocation is performed, and the string
/// is not copied.
Expand All @@ -3130,7 +3131,8 @@ impl<'a> From<&'a str> for Cow<'a, str> {

#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
impl<'a> From<String> for Cow<'a, str> {
#[rustc_const_unstable(feature = "const_from", issue = "143773")]
impl<'a> const From<String> for Cow<'a, str> {
/// Converts a [`String`] into an [`Owned`] variant.
/// No heap allocation is performed, and the string
/// is not copied.
Expand All @@ -3153,7 +3155,8 @@ impl<'a> From<String> for Cow<'a, str> {

#[cfg(not(no_global_oom_handling))]
#[stable(feature = "cow_from_string_ref", since = "1.28.0")]
impl<'a> From<&'a String> for Cow<'a, str> {
#[rustc_const_unstable(feature = "const_from", issue = "143773")]
impl<'a> const From<&'a String> for Cow<'a, str> {
/// Converts a [`String`] reference into a [`Borrowed`] variant.
/// No heap allocation is performed, and the string
/// is not copied.
Expand Down
12 changes: 8 additions & 4 deletions library/alloc/src/vec/cow.rs
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Expand Up @@ -2,7 +2,8 @@ use super::Vec;
use crate::borrow::Cow;

#[stable(feature = "cow_from_vec", since = "1.8.0")]
impl<'a, T: Clone> From<&'a [T]> for Cow<'a, [T]> {
#[rustc_const_unstable(feature = "const_from", issue = "143773")]
impl<'a, T: Clone> const From<&'a [T]> for Cow<'a, [T]> {
/// Creates a [`Borrowed`] variant of [`Cow`]
/// from a slice.
///
Expand All @@ -15,7 +16,8 @@ impl<'a, T: Clone> From<&'a [T]> for Cow<'a, [T]> {
}

#[stable(feature = "cow_from_array_ref", since = "1.77.0")]
impl<'a, T: Clone, const N: usize> From<&'a [T; N]> for Cow<'a, [T]> {
#[rustc_const_unstable(feature = "const_from", issue = "143773")]
impl<'a, T: Clone, const N: usize> const From<&'a [T; N]> for Cow<'a, [T]> {
/// Creates a [`Borrowed`] variant of [`Cow`]
/// from a reference to an array.
///
Expand All @@ -28,7 +30,8 @@ impl<'a, T: Clone, const N: usize> From<&'a [T; N]> for Cow<'a, [T]> {
}

#[stable(feature = "cow_from_vec", since = "1.8.0")]
impl<'a, T: Clone> From<Vec<T>> for Cow<'a, [T]> {
#[rustc_const_unstable(feature = "const_from", issue = "143773")]
impl<'a, T: Clone> const From<Vec<T>> for Cow<'a, [T]> {
/// Creates an [`Owned`] variant of [`Cow`]
/// from an owned instance of [`Vec`].
///
Expand All @@ -41,7 +44,8 @@ impl<'a, T: Clone> From<Vec<T>> for Cow<'a, [T]> {
}

#[stable(feature = "cow_from_vec_ref", since = "1.28.0")]
impl<'a, T: Clone> From<&'a Vec<T>> for Cow<'a, [T]> {
#[rustc_const_unstable(feature = "const_from", issue = "143773")]
impl<'a, T: Clone> const From<&'a Vec<T>> for Cow<'a, [T]> {
/// Creates a [`Borrowed`] variant of [`Cow`]
/// from a reference to [`Vec`].
///
Expand Down
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