From 688220582c94d129a2311ebd48ca69f28f4d8d07 Mon Sep 17 00:00:00 2001
From: moonie <67006455+Kim-Dewelski@users.noreply.github.com>
Date: Wed, 25 Sep 2024 20:49:04 +0200
Subject: [PATCH 1/4] added core::mem::reshape

---
 library/core/src/mem/mod.rs | 12 ++++++++++++
 library/core/tests/mem.rs   | 11 +++++++++++
 2 files changed, 23 insertions(+)

diff --git a/library/core/src/mem/mod.rs b/library/core/src/mem/mod.rs
index 414262fcf5ab1..693e4968ae114 100644
--- a/library/core/src/mem/mod.rs
+++ b/library/core/src/mem/mod.rs
@@ -874,6 +874,18 @@ pub const fn replace<T>(dest: &mut T, src: T) -> T {
     }
 }
 
+#[inline]
+#[unstable(feature = "mem_reshape", issue = "none")]
+pub fn reshape<T>(dest: &mut T, f: impl FnOnce(T) -> T) {
+    // SAFETY: We read from `dest` but directly write to it afterwards,
+    // such that the old value is not duplicated. Nothing is dropped and
+    // nothing here can panic.
+    unsafe {
+        let result = ptr::read(dest);
+        ptr::write(dest, f(result));
+    }
+}
+
 /// Disposes of a value.
 ///
 /// This does so by calling the argument's implementation of [`Drop`][drop].
diff --git a/library/core/tests/mem.rs b/library/core/tests/mem.rs
index f3b4387f6a898..ede4f4e971861 100644
--- a/library/core/tests/mem.rs
+++ b/library/core/tests/mem.rs
@@ -110,6 +110,17 @@ fn test_replace() {
     assert!(y.is_some());
 }
 
+#[test]
+fn test_reshape() {
+    let mut x = Some("test".to_string());
+    reshape(&mut x, |x| None);
+    assert!(x.is_none());
+
+    let mut y = "test".to_string();
+    reshape(&mut y, |y| y + "test");
+    assert_eq!(y, "testtest");
+}
+
 #[test]
 fn test_transmute_copy() {
     assert_eq!(1, unsafe { transmute_copy(&1) });

From ef3048ee20bdd896d8f0cce91a8a6888115481a3 Mon Sep 17 00:00:00 2001
From: moonie <67006455+Kim-Dewelski@users.noreply.github.com>
Date: Wed, 25 Sep 2024 20:59:57 +0200
Subject: [PATCH 2/4] added simple documentation

---
 library/core/src/mem/mod.rs | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/library/core/src/mem/mod.rs b/library/core/src/mem/mod.rs
index 693e4968ae114..f38eb0073aad5 100644
--- a/library/core/src/mem/mod.rs
+++ b/library/core/src/mem/mod.rs
@@ -874,6 +874,26 @@ pub const fn replace<T>(dest: &mut T, src: T) -> T {
     }
 }
 
+/// Replaces the value in `dest` by the value returned by `f`.
+///
+/// `f` receives the current referenced value of `dest` as its argument.
+///
+/// * If you want to replace the values of two variables, see [`swap`].
+/// * If you want to replace with a default value, see [`take`].
+/// * If you want replace without the function, see [`replace`].
+///
+/// # Examples
+///
+/// A simple example:
+///
+/// ```
+/// use std::mem;
+///
+/// let mut v: Vec<i32> = vec![1, 2];
+///
+/// mem::replace(&mut v, |mut v| { v.push(3); v });
+/// assert_eq!(vec![1, 2, 3], v);
+/// ```
 #[inline]
 #[unstable(feature = "mem_reshape", issue = "none")]
 pub fn reshape<T>(dest: &mut T, f: impl FnOnce(T) -> T) {

From d1169fde5ba9197ce3cbec795ea0e968ce71e516 Mon Sep 17 00:00:00 2001
From: moonie <67006455+Kim-Dewelski@users.noreply.github.com>
Date: Wed, 25 Sep 2024 21:00:48 +0200
Subject: [PATCH 3/4] added tracking issue

---
 library/core/src/mem/mod.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/library/core/src/mem/mod.rs b/library/core/src/mem/mod.rs
index f38eb0073aad5..67b6c79b7e32f 100644
--- a/library/core/src/mem/mod.rs
+++ b/library/core/src/mem/mod.rs
@@ -895,7 +895,7 @@ pub const fn replace<T>(dest: &mut T, src: T) -> T {
 /// assert_eq!(vec![1, 2, 3], v);
 /// ```
 #[inline]
-#[unstable(feature = "mem_reshape", issue = "none")]
+#[unstable(feature = "mem_reshape", issue = "130848")]
 pub fn reshape<T>(dest: &mut T, f: impl FnOnce(T) -> T) {
     // SAFETY: We read from `dest` but directly write to it afterwards,
     // such that the old value is not duplicated. Nothing is dropped and

From 9bd7cbecc66b521dd88765635f967e770162fd35 Mon Sep 17 00:00:00 2001
From: moonie <67006455+Kim-Dewelski@users.noreply.github.com>
Date: Wed, 25 Sep 2024 21:10:48 +0200
Subject: [PATCH 4/4] removed unused variable in test

---
 library/core/tests/mem.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/library/core/tests/mem.rs b/library/core/tests/mem.rs
index ede4f4e971861..5e2bdfda3700e 100644
--- a/library/core/tests/mem.rs
+++ b/library/core/tests/mem.rs
@@ -113,7 +113,7 @@ fn test_replace() {
 #[test]
 fn test_reshape() {
     let mut x = Some("test".to_string());
-    reshape(&mut x, |x| None);
+    reshape(&mut x, |_| None);
     assert!(x.is_none());
 
     let mut y = "test".to_string();