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Constantify some slice methods #83571

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Mar 30, 2021
Merged

Constantify some slice methods #83571

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24 changes: 16 additions & 8 deletions library/core/src/slice/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -145,8 +145,9 @@ impl<T> [T] {
/// assert_eq!(None, w.first());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
#[inline]
pub fn first(&self) -> Option<&T> {
pub const fn first(&self) -> Option<&T> {
if let [first, ..] = self { Some(first) } else { None }
}

Expand All @@ -163,8 +164,9 @@ impl<T> [T] {
/// assert_eq!(x, &[5, 1, 2]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
#[inline]
pub fn first_mut(&mut self) -> Option<&mut T> {
pub const fn first_mut(&mut self) -> Option<&mut T> {
if let [first, ..] = self { Some(first) } else { None }
}

Expand All @@ -181,8 +183,9 @@ impl<T> [T] {
/// }
/// ```
#[stable(feature = "slice_splits", since = "1.5.0")]
#[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
#[inline]
pub fn split_first(&self) -> Option<(&T, &[T])> {
pub const fn split_first(&self) -> Option<(&T, &[T])> {
if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
}

Expand All @@ -201,8 +204,9 @@ impl<T> [T] {
/// assert_eq!(x, &[3, 4, 5]);
/// ```
#[stable(feature = "slice_splits", since = "1.5.0")]
#[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
#[inline]
pub fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])> {
pub const fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])> {
if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
}

Expand All @@ -219,8 +223,9 @@ impl<T> [T] {
/// }
/// ```
#[stable(feature = "slice_splits", since = "1.5.0")]
#[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
#[inline]
pub fn split_last(&self) -> Option<(&T, &[T])> {
pub const fn split_last(&self) -> Option<(&T, &[T])> {
if let [init @ .., last] = self { Some((last, init)) } else { None }
}

Expand All @@ -239,8 +244,9 @@ impl<T> [T] {
/// assert_eq!(x, &[4, 5, 3]);
/// ```
#[stable(feature = "slice_splits", since = "1.5.0")]
#[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
#[inline]
pub fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])> {
pub const fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])> {
if let [init @ .., last] = self { Some((last, init)) } else { None }
}

Expand All @@ -256,8 +262,9 @@ impl<T> [T] {
/// assert_eq!(None, w.last());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
#[inline]
pub fn last(&self) -> Option<&T> {
pub const fn last(&self) -> Option<&T> {
if let [.., last] = self { Some(last) } else { None }
}

Expand All @@ -274,8 +281,9 @@ impl<T> [T] {
/// assert_eq!(x, &[0, 1, 10]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
#[inline]
pub fn last_mut(&mut self) -> Option<&mut T> {
pub const fn last_mut(&mut self) -> Option<&mut T> {
if let [.., last] = self { Some(last) } else { None }
}

Expand Down