Add tracking issue rust-lang#75243

Add note & example about iter order

Add doc changes

Update doc comments

Author: JulianKnodt

library/core/src/array/mod.rs

@@ -368,16 +368,23 @@ 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
 #[cfg(not(bootstrap))]
 #[lang = "array"]
 impl<T, const N: usize> [T; N] {
-    /// Returns an array of the same size as self, with `f` applied to each element.
+    /// Returns an array of the same size as `self`, with function `f` applied to each element.
+    /// The closure will be called on elements 0 up to but excluding N.
     ///
     /// # Examples
+    ///
     /// ```
     /// # #![feature(array_map)]
     /// let x = [1, 2, 3];
     /// let y = x.map(|v| v + 1);
     /// assert_eq!(y, [2, 3, 4]);
+    ///
+    /// let x = [1, 2, 3];
+    /// let mut temp = 0;
+    /// let y = x.map(|v| { temp += 1; v * temp });
+    /// assert_eq!(y, [1, 4, 9]);
     /// ```
-    #[unstable(feature = "array_map", issue = "77777")]
+    #[unstable(feature = "array_map", issue = "75243")]
     pub fn map<F, U>(self, mut f: F) -> [U; N]
     where
         F: FnMut(T) -> U,