Implement array::repeat

library/core/src/array/mod.rs

@@ -10,7 +10,7 @@ use crate::convert::Infallible;
 use crate::error::Error;
 use crate::fmt;
 use crate::hash::{self, Hash};
-use crate::iter::UncheckedIterator;
+use crate::iter::{repeat_n, UncheckedIterator};
 use crate::mem::{self, MaybeUninit};
 use crate::ops::{
     ChangeOutputType, ControlFlow, FromResidual, Index, IndexMut, NeverShortCircuit, Residual, Try,
@@ -27,6 +27,33 @@ pub(crate) use drain::drain_array_with;
 #[stable(feature = "array_value_iter", since = "1.51.0")]
 pub use iter::IntoIter;
 
+/// Creates an array of type `[T; N]` by repeatedly cloning a value.
+///
+/// This is the same as `[val; N]`, but it also works for types that do not
+/// implement [`Copy`].
+///
+/// The provided value will be used as an element of the resulting array and
+/// will be cloned N - 1 times to fill up the rest. If N is zero, the value
+/// will be dropped.
+///
+/// # Example
+///
+/// Creating muliple copies of a `String`:
+/// ```rust
+/// #![feature(array_repeat)]
+///
+/// use std::array;
+///
+/// let string = "Hello there!".to_string();
+/// let strings = array::repeat(string);
+/// assert_eq!(strings, ["Hello there!", "Hello there!"]);
+/// ```
+#[inline]
+#[unstable(feature = "array_repeat", issue = "126695")]
+pub fn repeat<T: Clone, const N: usize>(val: T) -> [T; N] {
+    from_trusted_iterator(repeat_n(val, N))
+}
+
 /// Creates an array of type [T; N], where each element `T` is the returned value from `cb`
 /// using that element's index.
 ///

library/core/src/iter/sources/repeat_n.rs

@@ -1,4 +1,4 @@
-use crate::iter::{FusedIterator, TrustedLen};
+use crate::iter::{FusedIterator, TrustedLen, UncheckedIterator};
 use crate::mem::ManuallyDrop;
 use crate::num::NonZero;
 
@@ -193,3 +193,5 @@ impl<A: Clone> FusedIterator for RepeatN<A> {}
 
 #[unstable(feature = "trusted_len", issue = "37572")]
 unsafe impl<A: Clone> TrustedLen for RepeatN<A> {}
+#[unstable(feature = "trusted_len_next_unchecked", issue = "37572")]
+impl<A: Clone> UncheckedIterator for RepeatN<A> {}

tests/codegen/array-repeat.rs

@@ -0,0 +1,15 @@
+//@ compile-flags: -O
+
+#![crate_type = "lib"]
+#![feature(array_repeat)]
+
+use std::array::repeat;
+
+// CHECK-LABEL: @byte_repeat
+#[no_mangle]
+fn byte_repeat(b: u8) -> [u8; 1024] {
+    // CHECK-NOT: alloca
+    // CHECK-NOT: store
+    // CHECK: memset
+    repeat(b)
+}