Rollup merge of #144515 - scottmcm:ptr_cast_array, r=Mark-Simulacrum

Implement `ptr_cast_array`
ACP: rust-lang/libs-team#602
Tracking Issue: #144514

Author: GuillaumeGomez

library/core/src/ptr/const_ptr.rs

@@ -1569,6 +1569,15 @@ impl<T> *const [T] {
 }
 }
 
+impl<T>*constT{
+/// Casts from a pointer-to-`T` to a pointer-to-`[T; N]`.
+#[inline]
+#[unstable(feature = "ptr_cast_array", issue = "144514")]
+pubconstfncast_array<constN:usize>(self) -> *const[T;N]{
+self.cast()
+}
+}
+
 impl<T,constN:usize>*const[T;N]{
 /// Returns a raw pointer to the array's buffer.
 ///

library/core/src/ptr/mut_ptr.rs

@@ -1990,6 +1990,15 @@ impl<T> *mut [T] {
 }
 }
 
+impl<T>*mutT{
+/// Casts from a pointer-to-`T` to a pointer-to-`[T; N]`.
+#[inline]
+#[unstable(feature = "ptr_cast_array", issue = "144514")]
+pubconstfncast_array<constN:usize>(self) -> *mut[T;N]{
+self.cast()
+}
+}
+
 impl<T,constN:usize>*mut[T;N]{
 /// Returns a raw pointer to the array's buffer.
 ///

library/core/src/ptr/non_null.rs

@@ -193,6 +193,13 @@ impl<T: Sized> NonNull<T> {
 // requirements for a reference.
 unsafe{&mut*self.cast().as_ptr()}
 }
+
+/// Casts from a pointer-to-`T` to a pointer-to-`[T; N]`.
+#[inline]
+#[unstable(feature = "ptr_cast_array", issue = "144514")]
+pubconstfncast_array<constN:usize>(self) -> NonNull<[T;N]>{
+self.cast()
+}
 }
 
 impl<T:PointeeSized>NonNull<T>{

library/core/src/slice/mod.rs

@@ -328,7 +328,7 @@ impl<T> [T] {
 }else{
 // SAFETY: We explicitly check for the correct number of elements,
 // and do not let the reference outlive the slice.
-Some(unsafe{&*(self.as_ptr().cast::<[T;N]>())})
+Some(unsafe{&*(self.as_ptr().cast_array())})
 }
 }
 
@@ -359,7 +359,7 @@ impl<T> [T] {
 // SAFETY: We explicitly check for the correct number of elements,
 // do not let the reference outlive the slice,
 // and require exclusive access to the entire slice to mutate the chunk.
-Some(unsafe{&mut*(self.as_mut_ptr().cast::<[T;N]>())})
+Some(unsafe{&mut*(self.as_mut_ptr().cast_array())})
 }
 }
 
@@ -387,7 +387,7 @@ impl<T> [T] {
 
 // SAFETY: We explicitly check for the correct number of elements,
 // and do not let the references outlive the slice.
-Some((unsafe{&*(first.as_ptr().cast::<[T;N]>())}, tail))
+Some((unsafe{&*(first.as_ptr().cast_array())}, tail))
 }
 
 /// Returns a mutable array reference to the first `N` items in the slice and the remaining
@@ -420,7 +420,7 @@ impl<T> [T] {
 // SAFETY: We explicitly check for the correct number of elements,
 // do not let the reference outlive the slice,
 // and enforce exclusive mutability of the chunk by the split.
-Some((unsafe{&mut*(first.as_mut_ptr().cast::<[T;N]>())}, tail))
+Some((unsafe{&mut*(first.as_mut_ptr().cast_array())}, tail))
 }
 
 /// Returns an array reference to the last `N` items in the slice and the remaining slice.
@@ -448,7 +448,7 @@ impl<T> [T] {
 
 // SAFETY: We explicitly check for the correct number of elements,
 // and do not let the references outlive the slice.
-Some((init,unsafe{&*(last.as_ptr().cast::<[T;N]>())}))
+Some((init,unsafe{&*(last.as_ptr().cast_array())}))
 }
 
 /// Returns a mutable array reference to the last `N` items in the slice and the remaining
@@ -482,7 +482,7 @@ impl<T> [T] {
 // SAFETY: We explicitly check for the correct number of elements,
 // do not let the reference outlive the slice,
 // and enforce exclusive mutability of the chunk by the split.
-Some((init,unsafe{&mut*(last.as_mut_ptr().cast::<[T;N]>())}))
+Some((init,unsafe{&mut*(last.as_mut_ptr().cast_array())}))
 }
 
 /// Returns an array reference to the last `N` items in the slice.
@@ -511,7 +511,7 @@ impl<T> [T] {
 
 // SAFETY: We explicitly check for the correct number of elements,
 // and do not let the references outlive the slice.
-Some(unsafe{&*(last.as_ptr().cast::<[T;N]>())})
+Some(unsafe{&*(last.as_ptr().cast_array())})
 }
 
 /// Returns a mutable array reference to the last `N` items in the slice.
@@ -542,7 +542,7 @@ impl<T> [T] {
 // SAFETY: We explicitly check for the correct number of elements,
 // do not let the reference outlive the slice,
 // and require exclusive access to the entire slice to mutate the chunk.
-Some(unsafe{&mut*(last.as_mut_ptr().cast::<[T;N]>())})
+Some(unsafe{&mut*(last.as_mut_ptr().cast_array())})
 }
 
 /// Returns a reference to an element or subslice depending on the type of
@@ -846,7 +846,7 @@ impl<T> [T] {
 #[must_use]
 pubconstfnas_array<constN:usize>(&self) -> Option<&[T;N]>{
 ifself.len() == N{
-let ptr = self.as_ptr()as*const[T;N];
+let ptr = self.as_ptr().cast_array();
 
 // SAFETY: The underlying array of a slice can be reinterpreted as an actual array `[T; N]` if `N` is not greater than the slice's length.
 let me = unsafe{&*ptr };
@@ -864,7 +864,7 @@ impl<T> [T] {
 #[must_use]
 pubconstfnas_mut_array<constN:usize>(&mutself) -> Option<&mut[T;N]>{
 ifself.len() == N{
-let ptr = self.as_mut_ptr()as*mut[T;N];
+let ptr = self.as_mut_ptr().cast_array();
 
 // SAFETY: The underlying array of a slice can be reinterpreted as an actual array `[T; N]` if `N` is not greater than the slice's length.
 let me = unsafe{&mut*ptr };