✨ First commit

.gitignore

@@ -0,0 +1,2 @@
+/target
+/Cargo.lock

Cargo.toml

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+[package]
+name = "veccell"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

src/lib.rs

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+use std::cell::{Cell, UnsafeCell};
+use std::fmt::{self, Debug};
+
+pub struct VecCell<T> {
+    mut_borrow: Cell<Option<usize>>,
+    borrows: Cell<usize>,
+    inner: Vec<UnsafeCell<T>>,
+}
+
+impl<T> VecCell<T> {
+    pub fn new() -> Self {
+        Self {
+            mut_borrow: Cell::new(None),
+            borrows: Cell::new(0),
+            inner: Vec::new(),
+        }
+    }
+
+    pub fn with_capacity(capacity: usize) -> Self {
+        Self {
+            mut_borrow: Cell::new(None),
+            borrows: Cell::new(0),
+            inner: Vec::with_capacity(capacity)
+        }
+    }
+
+    pub fn into_raw_parts(self) -> (Vec<UnsafeCell<T>>, Option<usize>, usize) {
+        (self.inner, self.mut_borrow.into_inner(), self.borrows.into_inner())
+    }
+
+    pub unsafe fn from_raw_parts(inner: Vec<UnsafeCell<T>>, mut_borrow: Option<usize>, borrows: usize) -> Self {
+        Self {
+            inner,
+            borrows: Cell::new(borrows),
+            mut_borrow: Cell::new(mut_borrow),
+        }
+    }
+
+    #[inline]
+    pub fn len(&self) -> usize {
+        self.inner.len()
+    }
+
+    pub fn borrows(&self) -> usize {
+        self.borrows.get()
+    }
+
+    pub fn mut_borrow(&self) -> Option<usize> {
+        self.mut_borrow.get()
+    }
+
+    pub fn push(&mut self, value: T) {
+        self.inner.push(UnsafeCell::new(value));
+    }
+
+    pub fn pop(&mut self) -> Option<T> {
+        debug_assert!(self.mut_borrow.get().is_none());
+        self.inner.pop().map(UnsafeCell::into_inner)
+    }
+
+    pub fn get<'b>(&'b self, index: usize) -> Option<VecRef<'b, T>> {
+        VecRef::new(self, index)
+    }
+
+    pub unsafe fn get_unchecked(&self, index: usize) -> &T {
+        &*self.inner.get_unchecked(index).get()
+    }
+
+    pub fn borrow_mut<'b>(&'b self, index: usize) -> Option<VecRefMut<'b, T>> {
+        VecRefMut::new(self, index)
+    }
+
+    pub fn get_mut(&mut self, index: usize) -> Option<&mut T> {
+        self.inner.get_mut(index).map(UnsafeCell::get_mut)
+    }
+
+    pub unsafe fn get_mut_unchecked(&self, index: usize) -> &mut T {
+        &mut *self.inner.get_unchecked(index).get()
+    }
+}
+
+pub struct VecRef<'a, T> {
+    borrows: &'a Cell<usize>,
+    value: &'a T,
+}
+
+impl<'a, T> VecRef<'a, T> {
+    fn new(vec: &'a VecCell<T>, index: usize) -> Option<Self> {
+        if vec.mut_borrow.get() == Some(index) {
+            return None
+        }
+
+        if index >= vec.len() {
+            return None
+        }
+
+        vec.borrows.set(vec.borrows.get().checked_add(1)?);
+
+        Some(Self {
+            borrows: &vec.borrows,
+            value: unsafe {
+                // SAFETY: there are no mutable borrows of vec.inner[index]
+                vec.get_unchecked(index)
+            }
+        })
+    }
+}
+
+impl<'a, T> std::ops::Deref for VecRef<'a, T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        self.value
+    }
+}
+
+impl<'a, T> Drop for VecRef<'a, T> {
+    #[inline]
+    fn drop(&mut self) {
+        debug_assert!(self.borrows.get() > 0, "Borrow count was null yet there was still a borrow!");
+        self.borrows.set(self.borrows.get() - 1);
+    }
+}
+
+impl<'a, T: Debug> Debug for VecRef<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("VecRef")
+            .field(self.value)
+            .finish()
+    }
+}
+
+pub struct VecRefMut<'a, T> {
+    mut_borrow: &'a Cell<Option<usize>>,
+    value: &'a mut T,
+}
+
+impl<'a, T> VecRefMut<'a, T> {
+    fn new(vec: &'a VecCell<T>, index: usize) -> Option<Self> {
+        if vec.borrows.get() > 0 || vec.mut_borrow.get().is_some() {
+            return None
+        }
+
+        if index >= vec.len() {
+            return None
+        }
+
+        vec.mut_borrow.set(Some(index));
+
+        Some(Self {
+            mut_borrow: &vec.mut_borrow,
+            value: unsafe {
+                // SAFETY: there are no mutable borrows of ∀x, vec.inner[x],
+                // and we set vec.mut_borrow to Some(index), guaranteeing no further aliasing
+                vec.get_mut_unchecked(index)
+            }
+        })
+    }
+}
+
+impl<'a, T> std::ops::Deref for VecRefMut<'a, T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        self.value
+    }
+}
+
+impl<'a, T> std::ops::DerefMut for VecRefMut<'a, T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        self.value
+    }
+}
+
+impl<'a, T> Drop for VecRefMut<'a, T> {
+    #[inline]
+    fn drop(&mut self) {
+        debug_assert!(self.mut_borrow.get().is_some());
+        self.mut_borrow.set(None);
+    }
+}
+
+impl<'a, T: Debug> Debug for VecRefMut<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("VecRefMut")
+            .field(self.value)
+            .finish()
+    }
+}