Initial implementation

Author: shamatar

library/core/src/array/mod.rs

@@ -389,6 +389,22 @@ array_impl_default! {32, T T T T T T T T T T T T T T T T T T T T T T T T T T T T
 
 #[lang = "array"]
 impl<T, const N: usize> [T; N] {
+    /// Returns the number of elements in the array.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(array_len)]
+    /// let a: [usize; 3] = [1, 2, 3];
+    /// assert_eq!(a.len(), 3);
+    /// ```
+    #[doc(alias = "length")]
+    #[unstable(feature = "array_len", issue = "none")]
+    #[inline]
+    pub const fn len(&self) -> usize {
+        N
+    }
+
     /// Returns an array of the same size as `self`, with function `f` applied to each element
     /// in order.
     ///

library/core/tests/array.rs

@@ -288,6 +288,12 @@ fn empty_array_is_always_default() {
     let _arr = <[DoesNotImplDefault; 0]>::default();
 }
 
+#[test]
+fn array_len() {
+    let a = [1, 2, 3];
+    assert_eq!(a.len(), 3);
+}
+
 #[test]
 fn array_map() {
     let a = [1, 2, 3];

library/core/tests/lib.rs

@@ -1,6 +1,7 @@
 #![feature(alloc_layout_extra)]
 #![feature(array_chunks)]
 #![feature(array_methods)]
+#![feature(array_len)]
 #![feature(array_map)]
 #![feature(array_windows)]
 #![feature(bool_to_option)]