| //@revisions: stack tree |
| //@[tree]compile-flags: -Zmiri-tree-borrows |
| #![allow(incomplete_features)] // for trait upcasting |
| #![feature(allocator_api, trait_upcasting)] |
| |
| use std::alloc::Layout; |
| use std::alloc::{AllocError, Allocator}; |
| use std::cell::Cell; |
| use std::mem::MaybeUninit; |
| use std::ptr::{self, NonNull}; |
| |
| struct OnceAlloc<'a> { |
| space: Cell<&'a mut [MaybeUninit<u8>]>, |
| } |
| |
| unsafe impl<'shared, 'a: 'shared> Allocator for &'shared OnceAlloc<'a> { |
| fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> { |
| let space = self.space.replace(&mut []); |
| |
| let (ptr, len) = (space.as_mut_ptr(), space.len()); |
| |
| if ptr.align_offset(layout.align()) != 0 || len < layout.size() { |
| return Err(AllocError); |
| } |
| |
| let slice_ptr = ptr::slice_from_raw_parts_mut(ptr as *mut u8, len); |
| unsafe { Ok(NonNull::new_unchecked(slice_ptr)) } |
| } |
| |
| unsafe fn deallocate(&self, _ptr: NonNull<u8>, _layout: Layout) {} |
| } |
| |
| trait MyTrait { |
| fn hello(&self) -> u8; |
| } |
| |
| impl MyTrait for [u8; 1] { |
| fn hello(&self) -> u8 { |
| self[0] |
| } |
| } |
| |
| trait TheTrait: MyTrait {} |
| |
| impl TheTrait for [u8; 1] {} |
| |
| /// `Box<T, G>` is a `ScalarPair` where the 2nd component is the allocator. |
| fn test1() { |
| let mut space = vec![MaybeUninit::new(0); 1]; |
| let once_alloc = OnceAlloc { space: Cell::new(&mut space[..]) }; |
| |
| let boxed = Box::new_in([42u8; 1], &once_alloc); |
| let _val = *boxed; |
| let with_dyn: Box<dyn TheTrait, &OnceAlloc> = boxed; |
| assert_eq!(42, with_dyn.hello()); |
| let with_dyn: Box<dyn MyTrait, &OnceAlloc> = with_dyn; // upcast |
| assert_eq!(42, with_dyn.hello()); |
| } |
| |
| // Make the allocator itself so big that the Box is not even a ScalarPair any more. |
| struct OnceAllocRef<'s, 'a>(&'s OnceAlloc<'a>, #[allow(dead_code)] u64); |
| |
| unsafe impl<'shared, 'a: 'shared> Allocator for OnceAllocRef<'shared, 'a> { |
| fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> { |
| self.0.allocate(layout) |
| } |
| |
| unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) { |
| self.0.deallocate(ptr, layout) |
| } |
| } |
| |
| /// `Box<T, G>` is an `Aggregate`. |
| fn test2() { |
| let mut space = vec![MaybeUninit::new(0); 1]; |
| let once_alloc = OnceAlloc { space: Cell::new(&mut space[..]) }; |
| |
| let boxed = Box::new_in([42u8; 1], OnceAllocRef(&once_alloc, 0)); |
| let _val = *boxed; |
| let with_dyn: Box<dyn TheTrait, OnceAllocRef> = boxed; |
| assert_eq!(42, with_dyn.hello()); |
| let with_dyn: Box<dyn MyTrait, OnceAllocRef> = with_dyn; // upcast |
| assert_eq!(42, with_dyn.hello()); |
| } |
| |
| fn main() { |
| test1(); |
| test2(); |
| } |