Auto merge of rust-lang#130829 - Urgau:option_array_transpose, r=ibra…

…heemdev

Add `[Option<T>; N]::transpose`

This PR as a new unstable libs API, `[Option<T>; N]::transpose`, which permits going from `[Option<T>; N]` to `Option<[T; N]>`.

This new API doesn't have an ACP as it was directly asked by T-libs-api in rust-lang#97601 (comment):

> [..] but it'd be trivial to provide a helper method `.transpose()` that turns array-of-Option into Option-of-array (**and we think that method should exist**; it already does for array-of-MaybeUninit).

r? libs

library/core/src/option.rs

@@ -2543,3 +2543,27 @@ impl<T> Option<Option<T>> {
         }
     }
 }
+
+impl<T, const N: usize> [Option<T>; N] {
+    /// Transposes a `[Option<T>; N]` into a `Option<[T; N]>`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(option_array_transpose)]
+    /// # use std::option::Option;
+    ///
+    /// let data = [Some(0); 1000];
+    /// let data: Option<[u8; 1000]> = data.transpose();
+    /// assert_eq!(data, Some([0; 1000]));
+    ///
+    /// let data = [Some(0), None];
+    /// let data: Option<[u8; 2]> = data.transpose();
+    /// assert_eq!(data, None);
+    /// ```
+    #[inline]
+    #[unstable(feature = "option_array_transpose", issue = "130828")]
+    pub fn transpose(self) -> Option<[T; N]> {
+        self.try_map(core::convert::identity)
+    }
+}