1 // SPDX-License-Identifier: Apache-2.0 OR MIT 2 3 #[cfg(all(feature = "alloc", not(feature = "std")))] 4 use alloc::{boxed::Box, sync::Arc}; 5 #[cfg(feature = "alloc")] 6 use core::alloc::AllocError; 7 use core::{mem::MaybeUninit, pin::Pin}; 8 #[cfg(feature = "std")] 9 use std::sync::Arc; 10 11 #[cfg(not(feature = "alloc"))] 12 type AllocError = core::convert::Infallible; 13 14 use crate::{ 15 init_from_closure, pin_init_from_closure, InPlaceWrite, Init, PinInit, ZeroableOption, 16 }; 17 18 pub extern crate alloc; 19 20 // SAFETY: All zeros is equivalent to `None` (option layout optimization guarantee: 21 // <https://doc.rust-lang.org/stable/std/option/index.html#representation>). 22 unsafe impl<T> ZeroableOption for Box<T> {} 23 24 /// Smart pointer that can initialize memory in-place. 25 pub trait InPlaceInit<T>: Sized { 26 /// Use the given pin-initializer to pin-initialize a `T` inside of a new smart pointer of this 27 /// type. 28 /// 29 /// If `T: !Unpin` it will not be able to move afterwards. 30 fn try_pin_init<E>(init: impl PinInit<T, E>) -> Result<Pin<Self>, E> 31 where 32 E: From<AllocError>; 33 34 /// Use the given pin-initializer to pin-initialize a `T` inside of a new smart pointer of this 35 /// type. 36 /// 37 /// If `T: !Unpin` it will not be able to move afterwards. 38 #[inline] 39 fn pin_init(init: impl PinInit<T>) -> Result<Pin<Self>, AllocError> { 40 // SAFETY: We delegate to `init` and only change the error type. 41 let init = unsafe { 42 pin_init_from_closure(|slot| match init.__init(slot) { 43 Ok(()) => Ok(()), 44 Err(i) => match i {}, 45 }) 46 }; 47 Self::try_pin_init(init) 48 } 49 50 /// Use the given initializer to in-place initialize a `T`. 51 fn try_init<E>(init: impl Init<T, E>) -> Result<Self, E> 52 where 53 E: From<AllocError>; 54 55 /// Use the given initializer to in-place initialize a `T`. 56 #[inline] 57 fn init(init: impl Init<T>) -> Result<Self, AllocError> { 58 // SAFETY: We delegate to `init` and only change the error type. 59 let init = unsafe { 60 init_from_closure(|slot| match init.__init(slot) { 61 Ok(()) => Ok(()), 62 Err(i) => match i {}, 63 }) 64 }; 65 Self::try_init(init) 66 } 67 } 68 69 #[cfg(feature = "alloc")] 70 macro_rules! try_new_uninit { 71 ($type:ident) => { 72 $type::try_new_uninit()? 73 }; 74 } 75 #[cfg(all(feature = "std", not(feature = "alloc")))] 76 macro_rules! try_new_uninit { 77 ($type:ident) => { 78 $type::new_uninit() 79 }; 80 } 81 82 impl<T> InPlaceInit<T> for Box<T> { 83 #[inline] 84 fn try_pin_init<E>(init: impl PinInit<T, E>) -> Result<Pin<Self>, E> 85 where 86 E: From<AllocError>, 87 { 88 try_new_uninit!(Box).write_pin_init(init) 89 } 90 91 #[inline] 92 fn try_init<E>(init: impl Init<T, E>) -> Result<Self, E> 93 where 94 E: From<AllocError>, 95 { 96 try_new_uninit!(Box).write_init(init) 97 } 98 } 99 100 impl<T> InPlaceInit<T> for Arc<T> { 101 #[inline] 102 fn try_pin_init<E>(init: impl PinInit<T, E>) -> Result<Pin<Self>, E> 103 where 104 E: From<AllocError>, 105 { 106 let mut this = try_new_uninit!(Arc); 107 let Some(slot) = Arc::get_mut(&mut this) else { 108 // SAFETY: the Arc has just been created and has no external references 109 unsafe { core::hint::unreachable_unchecked() } 110 }; 111 let slot = slot.as_mut_ptr(); 112 // SAFETY: When init errors/panics, slot will get deallocated but not dropped, 113 // slot is valid and will not be moved, because we pin it later. 114 unsafe { init.__init(slot)? }; 115 // SAFETY: All fields have been initialized and this is the only `Arc` to that data. 116 Ok(unsafe { Pin::new_unchecked(this.assume_init()) }) 117 } 118 119 #[inline] 120 fn try_init<E>(init: impl Init<T, E>) -> Result<Self, E> 121 where 122 E: From<AllocError>, 123 { 124 let mut this = try_new_uninit!(Arc); 125 let Some(slot) = Arc::get_mut(&mut this) else { 126 // SAFETY: the Arc has just been created and has no external references 127 unsafe { core::hint::unreachable_unchecked() } 128 }; 129 let slot = slot.as_mut_ptr(); 130 // SAFETY: When init errors/panics, slot will get deallocated but not dropped, 131 // slot is valid. 132 unsafe { init.__init(slot)? }; 133 // SAFETY: All fields have been initialized. 134 Ok(unsafe { this.assume_init() }) 135 } 136 } 137 138 impl<T> InPlaceWrite<T> for Box<MaybeUninit<T>> { 139 type Initialized = Box<T>; 140 141 #[inline] 142 fn write_init<E>(mut self, init: impl Init<T, E>) -> Result<Self::Initialized, E> { 143 let slot = self.as_mut_ptr(); 144 // SAFETY: When init errors/panics, slot will get deallocated but not dropped, 145 // slot is valid. 146 unsafe { init.__init(slot)? }; 147 // SAFETY: All fields have been initialized. 148 Ok(unsafe { self.assume_init() }) 149 } 150 151 #[inline] 152 fn write_pin_init<E>(mut self, init: impl PinInit<T, E>) -> Result<Pin<Self::Initialized>, E> { 153 let slot = self.as_mut_ptr(); 154 // SAFETY: When init errors/panics, slot will get deallocated but not dropped, 155 // slot is valid and will not be moved, because we pin it later. 156 unsafe { init.__init(slot)? }; 157 // SAFETY: All fields have been initialized. 158 Ok(unsafe { self.assume_init() }.into()) 159 } 160 } 161