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use core::{
alloc::Layout,
mem::MaybeUninit,
ops::{Deref, DerefMut},
ptr::Pointee,
};
use std::fmt::Debug;
use crate::{context::Mutation, gc::Gc, gc_box::GcBox, Collect, Invariant};
/// A thin, garbage collected pointer type, which is guaranteed to be unique.
pub struct UniqueGc<'b, T: ?Sized>(GcBox<T>, Invariant<'b>);
impl<'b, T> UniqueGc<'b, T> {
/// Allocates garbage collected memory on the heap and then places `val`
/// into it.
///
/// This allocates regardless of if `T` is zero-sized.
///
/// # Examples
/// ```
/// # use ghost_gc::{once_arena, UniqueGc};
/// # once_arena(|mt| {
/// let five = UniqueGc::new(5, mt);
/// # });
/// ```
pub fn new(val: T, mt: &Mutation<'b>) -> UniqueGc<'b, T>
where
T: Collect,
{
let inner = mt.allocate::<T>((), Layout::new::<T>());
// .context()
// .allocate::<T>((), Layout::new::<T>(), mt.alloc());
// Safety: No references exist, as the pointer was just created.
unsafe { inner.data_ptr().write(val) };
// Safety: The value was just written.
unsafe { inner.set_init() };
UniqueGc(inner, Invariant)
}
/// Constructs a new garbage collected pointer with uninitialized contents.
///
/// # Examples
/// ```
/// # use ghost_gc::{once_arena, UniqueGc};
/// # once_arena(|mt| {
/// let mut five = UniqueGc::<u32>::new_uninit(mt);
///
/// let five = unsafe {
/// five.as_mut_ptr().write(5);
///
/// five.assume_init()
/// };
///
/// assert_eq!(*five, 5);
/// # });
/// ```
pub fn new_uninit(mt: &Mutation<'b>) -> UniqueGc<'b, MaybeUninit<T>> {
UniqueGc::new(MaybeUninit::uninit(), mt)
}
/// Constructs a new garbage collected pointer with uninitialized contents,
/// with the memory being filled with `0` bytes.
///
/// See [`MaybeUninit::zeroed`] for examples of correct and incorrect usage
/// of this method.
///
/// # Examples
/// ```
/// # use ghost_gc::{once_arena, UniqueGc};
/// # once_arena(|mt| {
/// let zero = UniqueGc::<u32>::new_zeroed(mt);
/// let zero = unsafe { zero.assume_init() };
///
/// assert_eq!(*zero, 0);
/// # });
/// ```
pub fn new_zeroed(mt: &Mutation<'b>) -> UniqueGc<'b, MaybeUninit<T>> {
UniqueGc::new(MaybeUninit::zeroed(), mt)
}
}
impl<'b, T> UniqueGc<'b, [T]> {
/// Constructs a new garbage collected slice with uninitialized contents.
///
/// # Examples
/// ```
/// # use ghost_gc::{once_arena, UniqueGc};
/// # once_arena(|mt| {
/// let mut values = UniqueGc::<[u32]>::new_uninit_slice(3, mt);
///
/// let values = unsafe {
/// values[0].as_mut_ptr().write(1);
/// values[1].as_mut_ptr().write(2);
/// values[2].as_mut_ptr().write(3);
///
/// values.assume_init()
/// };
///
/// assert_eq!(*values, [1, 2, 3]);
/// # });
/// ```
pub fn new_uninit_slice(len: usize, mt: &Mutation<'b>) -> UniqueGc<'b, [MaybeUninit<T>]> {
let inner = mt
.context()
.allocate::<[MaybeUninit<T>]>(len, Layout::array::<T>(len).unwrap());
unsafe { inner.set_init() };
UniqueGc(inner, Invariant)
}
/// Constructs a new garbage collected slice with uninitialized contents, with the memory being
/// filled with `0` bytes.
///
/// See [`MaybeUninit::zeroed`] for examples of correct and incorrect usage of this method.
///
/// # Examples
/// ```
/// # use ghost_gc::{once_arena, UniqueGc};
/// # once_arena(|mt| {
/// let values = UniqueGc::<[u32]>::new_zeroed_slice(3, mt);
/// let values = unsafe { values.assume_init() };
///
/// assert_eq!(*values, [0, 0, 0]);
/// # });
/// ```
pub fn new_zeroed_slice(len: usize, mt: &Mutation<'b>) -> UniqueGc<'b, [MaybeUninit<T>]> {
let inner = mt
.context()
.allocate::<[MaybeUninit<T>]>(len, Layout::array::<T>(len).unwrap());
unsafe { core::ptr::write_bytes(inner.data_ptr().cast::<T>(), 0, len) };
unsafe { inner.set_init() };
UniqueGc(inner, Invariant)
}
}
impl<'b> UniqueGc<'b, str> {
/// Constructs a new garbage collected string, copied from the passed value.
///
/// ```
/// # use ghost_gc::{once_arena, UniqueGc};
/// # once_arena(|mt| {
/// let s = UniqueGc::from_str("Hello, World!", mt);
/// assert_eq!(&*s, "Hello, World!");
/// # });
/// ```
pub fn from_str(s: &str, mt: &Mutation<'b>) -> UniqueGc<'b, str> {
let mut gc = UniqueGc::<[u8]>::new_uninit_slice(s.len(), mt);
unsafe { std::ptr::copy_nonoverlapping(s.as_ptr(), gc.as_mut_ptr().cast(), s.len()) };
unsafe { gc.transmute() }
}
}
impl<'b, T: Collect> UniqueGc<'b, MaybeUninit<T>> {
/// Converts to `UniqueGc<'b, T>`.
///
/// # Safety
/// As with [`MaybeUninit::assume_init`], it is up to the caller to
/// guarantee that the value really is in an initialized state. Calling
/// this when the content is not yet fully initialized causes immediate
/// undefined behaviour.
///
/// # Examples
/// ```
/// # use ghost_gc::{once_arena, UniqueGc};
/// # once_arena(|mt| {
/// let mut five = UniqueGc::<u32>::new_uninit(mt);
///
/// let five = unsafe {
/// five.as_mut_ptr().write(5);
///
/// five.assume_init()
/// };
///
/// assert_eq!(*five, 5);
/// # });
/// ```
pub unsafe fn assume_init(self) -> UniqueGc<'b, T> {
unsafe { self.transmute() }
}
/// Writes the value and converts to `UniqueGc<'b, T>`.
///
/// This method converts the pointer similarly to [`UniqueGc::assume_init`],
/// but writes `value` into it before the conversion, thus guaranteeing safety.
/// In some scenarios use of this method may improve performance because the
/// compiler may be able to optimize copying from stack.
pub fn write(mut self, value: T) -> UniqueGc<'b, T> {
(*self).write(value);
unsafe { self.assume_init() }
}
}
impl<'b, T: Collect> UniqueGc<'b, [MaybeUninit<T>]> {
/// Converts to `Gc<'b, [T]>`.
///
/// # Safety
/// As with [`MaybeUninit::assume_init`], it is up to the caller to guarantee that the values
/// really are in an initialized state. Calling this when the content is not yet fully
/// initialized causes immediate undefined behaviour.
///
/// # Examples
/// ```
/// # use ghost_gc::{once_arena, UniqueGc};
/// # once_arena(|mt| {
/// let mut values = UniqueGc::<[u32]>::new_uninit_slice(3, mt);
///
/// let values = unsafe {
/// values[0].as_mut_ptr().write(1);
/// values[1].as_mut_ptr().write(2);
/// values[2].as_mut_ptr().write(3);
///
/// values.assume_init()
/// };
///
/// assert_eq!(*values, [1, 2, 3]);
/// # });
/// ```
pub unsafe fn assume_init(self) -> UniqueGc<'b, [T]> {
unsafe { self.transmute::<[T]>() }
}
}
impl<'b, T: ?Sized> UniqueGc<'b, T> {
/// Converts the `UniqueGc` into a regular [`Gc`].
///
/// This consumes the `UniqueGc` and returns a regular [`Gc`] which points to the same data
/// as the `UniqueGc`.
///
/// # Examples
/// ```
/// # use ghost_gc::{once_arena, UniqueGc, Gc};
/// # once_arena(|mt| {
/// let gc: Gc<u32> = UniqueGc::into_gc(UniqueGc::new(5, mt));
/// # });
/// ```
pub fn into_gc(this: Self) -> Gc<'b, T> {
unsafe { Gc::from_box(this.0) }
}
pub fn as_ptr(&self) -> *const T {
self.0.data_ptr()
}
pub fn as_ptr_mut(&mut self) -> *mut T {
self.0.data_ptr()
}
// /// Consumes the `UniqueGc`, returning a raw pointer.
// ///
// /// The resultant pointer is only guaranteed to point to an allocation for the remainder of
// /// [`Arena::view`] closure.
// pub(crate) fn into_box(self) -> GcBox<T> {
// self.0
// }
// /// Constructs a `UniqueGc` from a raw pointer.
// ///
// /// # Safety
// /// The pointer must have come from a previous call to [`UniqueGc::into_raw`].
// pub(crate) unsafe fn from_box(ptr: GcBox<T>) -> UniqueGc<'b, T> {
// UniqueGc(ptr, PhantomData)
// }
/// # Safety
/// Layouts have to match, pointed to data has to match.
pub(crate) unsafe fn transmute<U: ?Sized + Collect>(self) -> UniqueGc<'b, U> {
debug_assert_eq!(
Layout::new::<<T as Pointee>::Metadata>(),
Layout::new::<<U as Pointee>::Metadata>(),
);
UniqueGc::<'b, U>(unsafe { self.0.transmute::<U>() }, Invariant)
}
}
impl<T: ?Sized> Deref for UniqueGc<'_, T> {
type Target = T;
fn deref(&self) -> &Self::Target {
unsafe { self.0.data() }
}
}
impl<T: ?Sized> DerefMut for UniqueGc<'_, T> {
fn deref_mut(&mut self) -> &mut Self::Target {
unsafe { self.0.data_mut() }
}
}
unsafe impl<T: ?Sized> Collect for UniqueGc<'_, T> {
const NEEDS_TRACE: bool = true;
fn trace(&self, c: &crate::Collector) {
use crate::gc_box::Colour;
match self.0.colour() {
Colour::Gray | Colour::White | Colour::Weak => {
unsafe { self.0.set_colour(Colour::Gray) };
c.context().push_box(self.0.erase());
}
Colour::Black => {}
}
}
}
impl<T: ?Sized + Debug> Debug for UniqueGc<'_, T> {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
(**self).fmt(f)
}
}
impl<T: ?Sized + PartialEq> PartialEq for UniqueGc<'_, T> {
fn eq(&self, other: &Self) -> bool {
(**self) == (**other)
}
}
impl<T: ?Sized + Eq> Eq for UniqueGc<'_, T> {}
impl<T: ?Sized + PartialOrd> PartialOrd for UniqueGc<'_, T> {
fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
(**self).partial_cmp(other)
}
}
impl<T: ?Sized + Ord> Ord for UniqueGc<'_, T> {
fn cmp(&self, other: &Self) -> std::cmp::Ordering {
(**self).cmp(other)
}
}
impl<T: ?Sized + std::hash::Hash> std::hash::Hash for UniqueGc<'_, T> {
fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
(**self).hash(state);
}
}