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|
//! Implement Fallible Box
use super::TryClone;
use crate::TryReserveError;
use alloc::alloc::Layout;
use alloc::boxed::Box;
use core::borrow::Borrow;
use core::ptr::NonNull;
/// 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> {
pub fn try_new(t: T) -> Result<Self, TryReserveError> {
Ok(Self {
inner: Box::try_new(t)?,
})
}
pub fn into_raw(b: TryBox<T>) -> *mut T {
Box::into_raw(b.inner)
}
/// # Safety
///
/// See std::boxed::from_raw
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)
}
}
fn alloc(layout: Layout) -> Result<NonNull<u8>, TryReserveError> {
#[cfg(feature = "unstable")] // requires allocator_api
{
use core::alloc::AllocRef as _;
let mut g = alloc::alloc::Global;
g.alloc(layout, alloc::alloc::AllocInit::Uninitialized)
.map_err(|_e| TryReserveError::AllocError {
layout,
non_exhaustive: (),
})
.map(|memory_block| memory_block.ptr)
}
#[cfg(not(feature = "unstable"))]
{
match layout.size() {
0 => {
// Required for alloc safety
// See https://doc.rust-lang.org/stable/std/alloc/trait.GlobalAlloc.html#safety-1
Ok(NonNull::dangling())
}
1..=core::usize::MAX => {
let ptr = unsafe { alloc::alloc::alloc(layout) };
core::ptr::NonNull::new(ptr).ok_or(TryReserveError::AllocError { layout })
}
_ => unreachable!("size must be non-negative"),
}
}
}
impl<T> FallibleBox<T> for Box<T> {
fn try_new(t: T) -> Result<Self, TryReserveError> {
let layout = Layout::for_value(&t);
let ptr = alloc(layout)?.as_ptr() as *mut T;
unsafe {
core::ptr::write(ptr, t);
Ok(Box::from_raw(ptr))
}
}
}
impl<T: TryClone> TryClone for Box<T> {
fn try_clone(&self) -> Result<Self, TryReserveError> {
Self::try_new(Borrow::<T>::borrow(self).try_clone()?)
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn boxed() {
let mut v = Box::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::try_new(()).expect("ok");
assert_eq!(b, Box::new(()));
}
}
|
