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. try_pin_init<E>(init: impl PinInit<T, E>) -> Result<Pin<Self>, E> where E: From<AllocError>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. pin_init(init: impl PinInit<T>) -> Result<Pin<Self>, AllocError>38 fn pin_init(init: impl PinInit<T>) -> Result<Pin<Self>, AllocError> { 39 // SAFETY: We delegate to `init` and only change the error type. 40 let init = unsafe { 41 pin_init_from_closure(|slot| match init.__pinned_init(slot) { 42 Ok(()) => Ok(()), 43 Err(i) => match i {}, 44 }) 45 }; 46 Self::try_pin_init(init) 47 } 48 49 /// Use the given initializer to in-place initialize a `T`. try_init<E>(init: impl Init<T, E>) -> Result<Self, E> where E: From<AllocError>50 fn try_init<E>(init: impl Init<T, E>) -> Result<Self, E> 51 where 52 E: From<AllocError>; 53 54 /// Use the given initializer to in-place initialize a `T`. init(init: impl Init<T>) -> Result<Self, AllocError>55 fn init(init: impl Init<T>) -> Result<Self, AllocError> { 56 // SAFETY: We delegate to `init` and only change the error type. 57 let init = unsafe { 58 init_from_closure(|slot| match init.__init(slot) { 59 Ok(()) => Ok(()), 60 Err(i) => match i {}, 61 }) 62 }; 63 Self::try_init(init) 64 } 65 } 66 67 #[cfg(feature = "alloc")] 68 macro_rules! try_new_uninit { 69 ($type:ident) => { 70 $type::try_new_uninit()? 71 }; 72 } 73 #[cfg(all(feature = "std", not(feature = "alloc")))] 74 macro_rules! try_new_uninit { 75 ($type:ident) => { 76 $type::new_uninit() 77 }; 78 } 79 80 impl<T> InPlaceInit<T> for Box<T> { 81 #[inline] try_pin_init<E>(init: impl PinInit<T, E>) -> Result<Pin<Self>, E> where E: From<AllocError>,82 fn try_pin_init<E>(init: impl PinInit<T, E>) -> Result<Pin<Self>, E> 83 where 84 E: From<AllocError>, 85 { 86 try_new_uninit!(Box).write_pin_init(init) 87 } 88 89 #[inline] try_init<E>(init: impl Init<T, E>) -> Result<Self, E> where E: From<AllocError>,90 fn try_init<E>(init: impl Init<T, E>) -> Result<Self, E> 91 where 92 E: From<AllocError>, 93 { 94 try_new_uninit!(Box).write_init(init) 95 } 96 } 97 98 impl<T> InPlaceInit<T> for Arc<T> { 99 #[inline] try_pin_init<E>(init: impl PinInit<T, E>) -> Result<Pin<Self>, E> where E: From<AllocError>,100 fn try_pin_init<E>(init: impl PinInit<T, E>) -> Result<Pin<Self>, E> 101 where 102 E: From<AllocError>, 103 { 104 let mut this = try_new_uninit!(Arc); 105 let Some(slot) = Arc::get_mut(&mut this) else { 106 // SAFETY: the Arc has just been created and has no external references 107 unsafe { core::hint::unreachable_unchecked() } 108 }; 109 let slot = slot.as_mut_ptr(); 110 // SAFETY: When init errors/panics, slot will get deallocated but not dropped, 111 // slot is valid and will not be moved, because we pin it later. 112 unsafe { init.__pinned_init(slot)? }; 113 // SAFETY: All fields have been initialized and this is the only `Arc` to that data. 114 Ok(unsafe { Pin::new_unchecked(this.assume_init()) }) 115 } 116 117 #[inline] try_init<E>(init: impl Init<T, E>) -> Result<Self, E> where E: From<AllocError>,118 fn try_init<E>(init: impl Init<T, E>) -> Result<Self, E> 119 where 120 E: From<AllocError>, 121 { 122 let mut this = try_new_uninit!(Arc); 123 let Some(slot) = Arc::get_mut(&mut this) else { 124 // SAFETY: the Arc has just been created and has no external references 125 unsafe { core::hint::unreachable_unchecked() } 126 }; 127 let slot = slot.as_mut_ptr(); 128 // SAFETY: When init errors/panics, slot will get deallocated but not dropped, 129 // slot is valid. 130 unsafe { init.__init(slot)? }; 131 // SAFETY: All fields have been initialized. 132 Ok(unsafe { this.assume_init() }) 133 } 134 } 135 136 impl<T> InPlaceWrite<T> for Box<MaybeUninit<T>> { 137 type Initialized = Box<T>; 138 write_init<E>(mut self, init: impl Init<T, E>) -> Result<Self::Initialized, E>139 fn write_init<E>(mut self, init: impl Init<T, E>) -> Result<Self::Initialized, E> { 140 let slot = self.as_mut_ptr(); 141 // SAFETY: When init errors/panics, slot will get deallocated but not dropped, 142 // slot is valid. 143 unsafe { init.__init(slot)? }; 144 // SAFETY: All fields have been initialized. 145 Ok(unsafe { self.assume_init() }) 146 } 147 write_pin_init<E>(mut self, init: impl PinInit<T, E>) -> Result<Pin<Self::Initialized>, E>148 fn write_pin_init<E>(mut self, init: impl PinInit<T, E>) -> Result<Pin<Self::Initialized>, E> { 149 let slot = self.as_mut_ptr(); 150 // SAFETY: When init errors/panics, slot will get deallocated but not dropped, 151 // slot is valid and will not be moved, because we pin it later. 152 unsafe { init.__pinned_init(slot)? }; 153 // SAFETY: All fields have been initialized. 154 Ok(unsafe { self.assume_init() }.into()) 155 } 156 } 157