add ref_cell projections

Author: BennoLossin

src/ops.rs

@@ -78,4 +78,5 @@ include!("./projections/maybe_uninit.rs");
 include!("./projections/non_null.rs");
 include!("./projections/pin.rs");
 include!("./projections/raw_ptr.rs");
+include!("./projections/ref_cell.rs");
 include!("./projections/unsafe_cell.rs");

src/projections/ref_cell.rs

@@ -0,0 +1,59 @@
+use core::cell::{Ref, RefMut};
+
+use crate::helper::project_ref;
+
+impl<T> Projectable for Ref<'_, T> {
+    type Inner = T;
+}
+
+impl<T> Projectable for RefMut<'_, T> {
+    type Inner = T;
+}
+
+unsafe impl<T> SafeProject for Ref<'_, T> {}
+unsafe impl<T> SafeProject for RefMut<'_, T> {}
+
+impl<'a, T, F> Project<F> for Ref<'a, T>
+where
+    F: Field<Base = T>,
+    F::Type: Sized + 'a,
+{
+    type Output<'b>
+        = Ref<'b, F::Type>
+    where
+        Self: 'b;
+    unsafe fn project<'b>(this: *const Self) -> Self::Output<'b>
+    where
+        Self: 'b,
+    {
+        let this = unsafe { &*this };
+        Ref::map(Ref::clone(this), |r| project_ref::<F>(r))
+    }
+}
+
+impl<'a, T, F> ProjectMut<F> for RefMut<'a, T>
+where
+    F: Field<Base = T>,
+    F::Type: Sized + 'a,
+{
+    type OutputMut<'b>
+        = RefMut<'b, F::Type>
+    where
+        Self: 'b;
+    unsafe fn project_mut<'b>(_this: *mut Self) -> Self::OutputMut<'b>
+    where
+        Self: 'b,
+    {
+        // this can't be implemented without being able to increment the mutable borrow count
+        // but it would look like the project for `Ref`
+        todo!("cannot be implemented outside of the stdlib")
+    }
+}
+
+unsafe impl<T> compat::ProjectableExt for Ref<'_, T> {
+    type Safety = compat::Safe;
+}
+
+unsafe impl<T> compat::ProjectableExt for RefMut<'_, T> {
+    type Safety = compat::Safe;
+}