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rust: pin-init: Implement `InPlaceWrite<T>` for `&'static mut MaybeUninit<T>`

PATCH Applied Benno Lossin 1 participant 2 messages Jan 8 – Jan 17

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Benno Lossin

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#0 lore raw

PATCH 1/1 rust: pin-init: Implement `InPlaceWrite<T>` for `&'static mut MaybeUninit<T>`

From: Oleksandr Babak <[email protected]>

This feature allows users to use &'static mut MaybeUninit<T> as a place to initialize the value. It mirrors an existing implemetation for Box<MaybeUninit>, but enables users to use external allocation mechanisms such as static_cell [1].

[ Added link to `static_cell` - Benno ]

---
This is the entire pin-init update this cycle. (excluding the syn patches, which I will send soon)

---
 rust/pin-init/src/lib.rs | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)
rust/pin-init/src/lib.rs +27 -0
index 8dc9dd5ac6fd..ea59c86a9108 100644
@@ -1536,6 +1536,33 @@ pub trait InPlaceWrite<T> {
     fn write_pin_init<E>(self, init: impl PinInit<T, E>) -> Result<Pin<Self::Initialized>, E>;
 }
 
+impl<T> InPlaceWrite<T> for &'static mut MaybeUninit<T> {
+    type Initialized = &'static mut T;
+
+    fn write_init<E>(self, init: impl Init<T, E>) -> Result<Self::Initialized, E> {
+        let slot = self.as_mut_ptr();
+
+        // SAFETY: `slot` is a valid pointer to uninitialized memory.
+        unsafe { init.__init(slot)? };
+
+        // SAFETY: The above call initialized the memory.
+        unsafe { Ok(self.assume_init_mut()) }
+    }
+
+    fn write_pin_init<E>(self, init: impl PinInit<T, E>) -> Result<Pin<Self::Initialized>, E> {
+        let slot = self.as_mut_ptr();
+
+        // SAFETY: `slot` is a valid pointer to uninitialized memory.
+        //
+        // The `'static` borrow guarantees the data will not be
+        // moved/invalidated until it gets dropped (which is never).
+        unsafe { init.__pinned_init(slot)? };
+
+        // SAFETY: The above call initialized the memory.
+        Ok(Pin::static_mut(unsafe { self.assume_init_mut() }))
+    }
+}
+
 /// Trait facilitating pinned destruction.
 ///
 /// Use [`pinned_drop`] to implement this trait safely:
Signature · 1 line
2.51.2
author maintainer Applied
#1 lore raw
Quoted 11 lines · Benno Lossin

From: Oleksandr Babak <[email protected]>

This feature allows users to use &'static mut MaybeUninit<T> as a place to initialize the value. It mirrors an existing implemetation for Box<MaybeUninit>, but enables users to use external allocation mechanisms such as static_cell [1].

[ Added link to `static_cell` - Benno ]
Quoted 6 lines

---
This is the entire pin-init update this cycle. (excluding the syn patches, which I will send soon)

---
 rust/pin-init/src/lib.rs | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

Applied to pin-init-next, thanks everyone!

Cheers,
Benno