Rollup merge of #75485 - RalfJung:pin, r=nagisa

[rust.git] / library / core / src / array / mod.rs

diff --git a/library/core/src/array/mod.rs b/library/core/src/array/mod.rs
index f85f5efbb9a3ce1265fb1f6eda117d394de04795..6b28ab7d755631f68860ed2cd402f9d1cb20c418 100644 (file)
--- a/library/core/src/array/mod.rs
+++ b/library/core/src/array/mod.rs
@@ -368,31 +368,43 @@ macro_rules! array_impl_default {
 #[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
+    /// in order.
     ///
     /// # Examples
+    ///
     /// ```
-    /// let x = [1,2,3];
+    /// #![feature(array_map)]
+    /// let x = [1, 2, 3];
     /// let y = x.map(|v| v + 1);
-    /// assert_eq!(y, [2,3,4]);
+    /// 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]);
+    ///
+    /// let x = ["Ferris", "Bueller's", "Day", "Off"];
+    /// let y = x.map(|v| v.len());
+    /// assert_eq!(y, [6, 9, 3, 3]);
     /// ```
-    #[unstable(feature = "array_map", issue = "77777")]
-    pub fn map<F, S>(self, mut f: F) -> [S; N]
+    #[unstable(feature = "array_map", issue = "75243")]
+    pub fn map<F, U>(self, mut f: F) -> [U; N]
     where
-        F: FnMut(T) -> S,
+        F: FnMut(T) -> U,
     {
         use crate::mem::MaybeUninit;
         struct Guard<T, const N: usize> {
             dst: *mut T,
-            curr_init: usize,
+            initialized: usize,
         }
 
         impl<T, const N: usize> Drop for Guard<T, N> {
             fn drop(&mut self) {
-                debug_assert!(self.curr_init <= N);
+                debug_assert!(self.initialized <= N);
 
                 let initialized_part =
-                    crate::ptr::slice_from_raw_parts_mut(self.dst, self.curr_init);
+                    crate::ptr::slice_from_raw_parts_mut(self.dst, self.initialized);
                 // SAFETY: this raw slice will contain only initialized objects
                 // that's why, it is allowed to drop it.
                 unsafe {
@@ -401,16 +413,17 @@ fn drop(&mut self) {
             }
         }
         let mut dst = MaybeUninit::uninit_array::<N>();
-        let mut guard: Guard<S, N> = Guard { dst: &mut dst as *mut _ as *mut S, curr_init: 0 };
-        for (i, e) in IntoIter::new(self).enumerate() {
-            dst[i] = MaybeUninit::new(f(e));
-            guard.curr_init += 1;
+        let mut guard: Guard<U, N> =
+            Guard { dst: MaybeUninit::first_ptr_mut(&mut dst), initialized: 0 };
+        for (src, dst) in IntoIter::new(self).zip(&mut dst) {
+            dst.write(f(src));
+            guard.initialized += 1;
         }
-        // FIXME convert to crate::mem::transmute when works with generics
-        // unsafe { crate::mem::transmute::<[MaybeUninit<S>; N], [S; N]>(dst) }
+        // FIXME: Convert to crate::mem::transmute once it works with generics.
+        // unsafe { crate::mem::transmute::<[MaybeUninit<U>; N], [U; N]>(dst) }
         crate::mem::forget(guard);
         // SAFETY: At this point we've properly initialized the whole array
-        // and we just need to cast it to the correct type
-        unsafe { (&mut dst as *mut _ as *mut [S; N]).read() }
+        // and we just need to cast it to the correct type.
+        unsafe { crate::mem::transmute_copy::<_, [U; N]>(&dst) }
     }
 }