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//! Implement Fallible Box
use super::TryClone;
use crate::TryReserveError;
use alloc::boxed::Box;
use core::borrow::Borrow;
use core::mem::ManuallyDrop;
use core::ops::Deref;
/// trait to implement Fallible Box
pub trait FallibleBox<T> {
/// try creating a new box, returning a Result<Box<T>,
/// TryReserveError> if allocation failed
fn try_new(t: T) -> Result<Self, TryReserveError>
where
Self: Sized;
}
/// TryBox is a thin wrapper around alloc::boxed::Box to provide support for
/// fallible allocation.
///
/// See the crate documentation for more.
pub struct TryBox<T> {
inner: Box<T>,
}
impl<T> TryBox<T> {
#[inline]
pub fn try_new(t: T) -> Result<Self, TryReserveError> {
Ok(Self {
inner: <Box<T> as FallibleBox<T>>::try_new(t)?,
})
}
#[inline(always)]
pub fn into_raw(b: TryBox<T>) -> *mut T {
Box::into_raw(b.inner)
}
/// # Safety
///
/// See std::boxed::from_raw
#[inline(always)]
pub unsafe fn from_raw(raw: *mut T) -> Self {
Self {
inner: Box::from_raw(raw),
}
}
}
impl<T: TryClone> TryClone for TryBox<T> {
fn try_clone(&self) -> Result<Self, TryReserveError> {
let clone: T = (*self.inner).try_clone()?;
Self::try_new(clone)
}
}
impl<T> Deref for TryBox<T> {
type Target = T;
#[inline(always)]
fn deref(&self) -> &T {
self.inner.deref()
}
}
impl<T> FallibleBox<T> for Box<T> {
fn try_new(t: T) -> Result<Self, TryReserveError> {
let mut vec = alloc::vec::Vec::new();
vec.try_reserve_exact(1)?;
vec.push(t);
// try_reserve_exact doesn't promise the exact size, but into_boxed_slice does.
// in practice the size is going to be okay anyway, so it won't realloc.
let ptr: *mut T = ManuallyDrop::new(vec.into_boxed_slice()).as_mut_ptr();
Ok(unsafe { Box::from_raw(ptr) })
}
}
impl<T: TryClone> TryClone for Box<T> {
#[inline]
fn try_clone(&self) -> Result<Self, TryReserveError> {
<Self as FallibleBox<T>>::try_new(Borrow::<T>::borrow(self).try_clone()?)
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn boxed() {
let mut v = <Box<_> as FallibleBox<_>>::try_new(5).unwrap();
assert_eq!(*v, 5);
*v = 3;
assert_eq!(*v, 3);
}
// #[test]
// fn big_alloc() {
// let layout = Layout::from_size_align(1_000_000_000_000, 8).unwrap();
// let ptr = unsafe { alloc::alloc::alloc(layout) };
// assert!(ptr.is_null());
// }
#[test]
fn trybox_zst() {
let b = <Box<_> as FallibleBox<_>>::try_new(()).expect("ok");
assert_eq!(b, Box::new(()));
}
struct NonCopyType;
#[test]
fn trybox_deref() {
let try_box: TryBox<NonCopyType> = TryBox::try_new(NonCopyType {}).unwrap();
let _derefed: &NonCopyType = try_box.deref();
}
#[test]
fn trybox_as_deref() {
let try_box_option: Option<TryBox<NonCopyType>> =
Some(TryBox::try_new(NonCopyType).unwrap());
let _ref_option: Option<&NonCopyType> = try_box_option.as_deref();
}
}