diff options
Diffstat (limited to 'rust/alloc/boxed.rs')
| -rw-r--r-- | rust/alloc/boxed.rs | 435 |
1 files changed, 419 insertions, 16 deletions
diff --git a/rust/alloc/boxed.rs b/rust/alloc/boxed.rs index 5e7518bffbfb..d4a03edd7d89 100644 --- a/rust/alloc/boxed.rs +++ b/rust/alloc/boxed.rs @@ -1,6 +1,6 @@ // SPDX-License-Identifier: Apache-2.0 OR MIT -//! A pointer type for heap allocation. +//! The `Box<T>` type for heap allocation. //! //! [`Box<T>`], casually referred to as a 'box', provides the simplest form of //! heap allocation in Rust. Boxes provide ownership for this allocation, and @@ -124,7 +124,21 @@ //! definition is just using `T*` can lead to undefined behavior, as //! described in [rust-lang/unsafe-code-guidelines#198][ucg#198]. //! +//! # Considerations for unsafe code +//! +//! **Warning: This section is not normative and is subject to change, possibly +//! being relaxed in the future! It is a simplified summary of the rules +//! currently implemented in the compiler.** +//! +//! The aliasing rules for `Box<T>` are the same as for `&mut T`. `Box<T>` +//! asserts uniqueness over its content. Using raw pointers derived from a box +//! after that box has been mutated through, moved or borrowed as `&mut T` +//! is not allowed. For more guidance on working with box from unsafe code, see +//! [rust-lang/unsafe-code-guidelines#326][ucg#326]. +//! +//! //! [ucg#198]: https://github.com/rust-lang/unsafe-code-guidelines/issues/198 +//! [ucg#326]: https://github.com/rust-lang/unsafe-code-guidelines/issues/326 //! [dereferencing]: core::ops::Deref //! [`Box::<T>::from_raw(value)`]: Box::from_raw //! [`Global`]: crate::alloc::Global @@ -139,6 +153,7 @@ use core::async_iter::AsyncIterator; use core::borrow; use core::cmp::Ordering; use core::convert::{From, TryFrom}; +use core::error::Error; use core::fmt; use core::future::Future; use core::hash::{Hash, Hasher}; @@ -163,6 +178,8 @@ use crate::raw_vec::RawVec; #[cfg(not(no_global_oom_handling))] use crate::str::from_boxed_utf8_unchecked; #[cfg(not(no_global_oom_handling))] +use crate::string::String; +#[cfg(not(no_global_oom_handling))] use crate::vec::Vec; #[cfg(not(no_thin))] @@ -196,12 +213,13 @@ impl<T> Box<T> { /// ``` /// let five = Box::new(5); /// ``` - #[cfg(not(no_global_oom_handling))] + #[cfg(all(not(no_global_oom_handling)))] #[inline(always)] #[stable(feature = "rust1", since = "1.0.0")] #[must_use] pub fn new(x: T) -> Self { - box x + #[rustc_box] + Box::new(x) } /// Constructs a new box with uninitialized contents. @@ -256,14 +274,21 @@ impl<T> Box<T> { Self::new_zeroed_in(Global) } - /// Constructs a new `Pin<Box<T>>`. If `T` does not implement `Unpin`, then + /// Constructs a new `Pin<Box<T>>`. If `T` does not implement [`Unpin`], then /// `x` will be pinned in memory and unable to be moved. + /// + /// Constructing and pinning of the `Box` can also be done in two steps: `Box::pin(x)` + /// does the same as <code>[Box::into_pin]\([Box::new]\(x))</code>. Consider using + /// [`into_pin`](Box::into_pin) if you already have a `Box<T>`, or if you want to + /// construct a (pinned) `Box` in a different way than with [`Box::new`]. #[cfg(not(no_global_oom_handling))] #[stable(feature = "pin", since = "1.33.0")] #[must_use] #[inline(always)] pub fn pin(x: T) -> Pin<Box<T>> { - (box x).into() + (#[rustc_box] + Box::new(x)) + .into() } /// Allocates memory on the heap then places `x` into it, @@ -543,8 +568,13 @@ impl<T, A: Allocator> Box<T, A> { unsafe { Ok(Box::from_raw_in(ptr.as_ptr(), alloc)) } } - /// Constructs a new `Pin<Box<T, A>>`. If `T` does not implement `Unpin`, then + /// Constructs a new `Pin<Box<T, A>>`. If `T` does not implement [`Unpin`], then /// `x` will be pinned in memory and unable to be moved. + /// + /// Constructing and pinning of the `Box` can also be done in two steps: `Box::pin_in(x, alloc)` + /// does the same as <code>[Box::into_pin]\([Box::new_in]\(x, alloc))</code>. Consider using + /// [`into_pin`](Box::into_pin) if you already have a `Box<T, A>`, or if you want to + /// construct a (pinned) `Box` in a different way than with [`Box::new_in`]. #[cfg(not(no_global_oom_handling))] #[unstable(feature = "allocator_api", issue = "32838")] #[rustc_const_unstable(feature = "const_box", issue = "92521")] @@ -926,6 +956,7 @@ impl<T: ?Sized> Box<T> { /// [`Layout`]: crate::Layout #[stable(feature = "box_raw", since = "1.4.0")] #[inline] + #[must_use = "call `drop(from_raw(ptr))` if you intend to drop the `Box`"] pub unsafe fn from_raw(raw: *mut T) -> Self { unsafe { Self::from_raw_in(raw, Global) } } @@ -1160,19 +1191,44 @@ impl<T: ?Sized, A: Allocator> Box<T, A> { unsafe { &mut *mem::ManuallyDrop::new(b).0.as_ptr() } } - /// Converts a `Box<T>` into a `Pin<Box<T>>` + /// Converts a `Box<T>` into a `Pin<Box<T>>`. If `T` does not implement [`Unpin`], then + /// `*boxed` will be pinned in memory and unable to be moved. /// /// This conversion does not allocate on the heap and happens in place. /// /// This is also available via [`From`]. - #[unstable(feature = "box_into_pin", issue = "62370")] + /// + /// Constructing and pinning a `Box` with <code>Box::into_pin([Box::new]\(x))</code> + /// can also be written more concisely using <code>[Box::pin]\(x)</code>. + /// This `into_pin` method is useful if you already have a `Box<T>`, or you are + /// constructing a (pinned) `Box` in a different way than with [`Box::new`]. + /// + /// # Notes + /// + /// It's not recommended that crates add an impl like `From<Box<T>> for Pin<T>`, + /// as it'll introduce an ambiguity when calling `Pin::from`. + /// A demonstration of such a poor impl is shown below. + /// + /// ```compile_fail + /// # use std::pin::Pin; + /// struct Foo; // A type defined in this crate. + /// impl From<Box<()>> for Pin<Foo> { + /// fn from(_: Box<()>) -> Pin<Foo> { + /// Pin::new(Foo) + /// } + /// } + /// + /// let foo = Box::new(()); + /// let bar = Pin::from(foo); + /// ``` + #[stable(feature = "box_into_pin", since = "1.63.0")] #[rustc_const_unstable(feature = "const_box", issue = "92521")] pub const fn into_pin(boxed: Self) -> Pin<Self> where A: 'static, { // It's not possible to move or replace the insides of a `Pin<Box<T>>` - // when `T: !Unpin`, so it's safe to pin it directly without any + // when `T: !Unpin`, so it's safe to pin it directly without any // additional requirements. unsafe { Pin::new_unchecked(boxed) } } @@ -1190,7 +1246,8 @@ unsafe impl<#[may_dangle] T: ?Sized, A: Allocator> Drop for Box<T, A> { impl<T: Default> Default for Box<T> { /// Creates a `Box<T>`, with the `Default` value for T. fn default() -> Self { - box T::default() + #[rustc_box] + Box::new(T::default()) } } @@ -1408,9 +1465,17 @@ impl<T: ?Sized, A: Allocator> const From<Box<T, A>> for Pin<Box<T, A>> where A: 'static, { - /// Converts a `Box<T>` into a `Pin<Box<T>>` + /// Converts a `Box<T>` into a `Pin<Box<T>>`. If `T` does not implement [`Unpin`], then + /// `*boxed` will be pinned in memory and unable to be moved. /// /// This conversion does not allocate on the heap and happens in place. + /// + /// This is also available via [`Box::into_pin`]. + /// + /// Constructing and pinning a `Box` with <code><Pin<Box\<T>>>::from([Box::new]\(x))</code> + /// can also be written more concisely using <code>[Box::pin]\(x)</code>. + /// This `From` implementation is useful if you already have a `Box<T>`, or you are + /// constructing a (pinned) `Box` in a different way than with [`Box::new`]. fn from(boxed: Box<T, A>) -> Self { Box::into_pin(boxed) } @@ -1422,7 +1487,7 @@ impl<T: Copy> From<&[T]> for Box<[T]> { /// Converts a `&[T]` into a `Box<[T]>` /// /// This conversion allocates on the heap - /// and performs a copy of `slice`. + /// and performs a copy of `slice` and its contents. /// /// # Examples /// ```rust @@ -1554,10 +1619,27 @@ impl<T, const N: usize> From<[T; N]> for Box<[T]> { /// println!("{boxed:?}"); /// ``` fn from(array: [T; N]) -> Box<[T]> { - box array + #[rustc_box] + Box::new(array) } } +/// Casts a boxed slice to a boxed array. +/// +/// # Safety +/// +/// `boxed_slice.len()` must be exactly `N`. +unsafe fn boxed_slice_as_array_unchecked<T, A: Allocator, const N: usize>( + boxed_slice: Box<[T], A>, +) -> Box<[T; N], A> { + debug_assert_eq!(boxed_slice.len(), N); + + let (ptr, alloc) = Box::into_raw_with_allocator(boxed_slice); + // SAFETY: Pointer and allocator came from an existing box, + // and our safety condition requires that the length is exactly `N` + unsafe { Box::from_raw_in(ptr as *mut [T; N], alloc) } +} + #[stable(feature = "boxed_slice_try_from", since = "1.43.0")] impl<T, const N: usize> TryFrom<Box<[T]>> for Box<[T; N]> { type Error = Box<[T]>; @@ -1573,13 +1655,46 @@ impl<T, const N: usize> TryFrom<Box<[T]>> for Box<[T; N]> { /// `boxed_slice.len()` does not equal `N`. fn try_from(boxed_slice: Box<[T]>) -> Result<Self, Self::Error> { if boxed_slice.len() == N { - Ok(unsafe { Box::from_raw(Box::into_raw(boxed_slice) as *mut [T; N]) }) + Ok(unsafe { boxed_slice_as_array_unchecked(boxed_slice) }) } else { Err(boxed_slice) } } } +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "boxed_array_try_from_vec", since = "1.66.0")] +impl<T, const N: usize> TryFrom<Vec<T>> for Box<[T; N]> { + type Error = Vec<T>; + + /// Attempts to convert a `Vec<T>` into a `Box<[T; N]>`. + /// + /// Like [`Vec::into_boxed_slice`], this is in-place if `vec.capacity() == N`, + /// but will require a reallocation otherwise. + /// + /// # Errors + /// + /// Returns the original `Vec<T>` in the `Err` variant if + /// `boxed_slice.len()` does not equal `N`. + /// + /// # Examples + /// + /// This can be used with [`vec!`] to create an array on the heap: + /// + /// ``` + /// let state: Box<[f32; 100]> = vec![1.0; 100].try_into().unwrap(); + /// assert_eq!(state.len(), 100); + /// ``` + fn try_from(vec: Vec<T>) -> Result<Self, Self::Error> { + if vec.len() == N { + let boxed_slice = vec.into_boxed_slice(); + Ok(unsafe { boxed_slice_as_array_unchecked(boxed_slice) }) + } else { + Err(vec) + } + } +} + impl<A: Allocator> Box<dyn Any, A> { /// Attempt to downcast the box to a concrete type. /// @@ -1973,8 +2088,7 @@ impl<T: ?Sized, A: Allocator> AsMut<T> for Box<T, A> { * could have a method to project a Pin<T> from it. */ #[stable(feature = "pin", since = "1.33.0")] -#[rustc_const_unstable(feature = "const_box", issue = "92521")] -impl<T: ?Sized, A: Allocator> const Unpin for Box<T, A> where A: 'static {} +impl<T: ?Sized, A: Allocator> Unpin for Box<T, A> where A: 'static {} #[unstable(feature = "generator_trait", issue = "43122")] impl<G: ?Sized + Generator<R> + Unpin, R, A: Allocator> Generator<R> for Box<G, A> @@ -2026,3 +2140,292 @@ impl<S: ?Sized + AsyncIterator + Unpin> AsyncIterator for Box<S> { (**self).size_hint() } } + +impl dyn Error { + #[inline] + #[stable(feature = "error_downcast", since = "1.3.0")] + #[rustc_allow_incoherent_impl] + /// Attempts to downcast the box to a concrete type. + pub fn downcast<T: Error + 'static>(self: Box<Self>) -> Result<Box<T>, Box<dyn Error>> { + if self.is::<T>() { + unsafe { + let raw: *mut dyn Error = Box::into_raw(self); + Ok(Box::from_raw(raw as *mut T)) + } + } else { + Err(self) + } + } +} + +impl dyn Error + Send { + #[inline] + #[stable(feature = "error_downcast", since = "1.3.0")] + #[rustc_allow_incoherent_impl] + /// Attempts to downcast the box to a concrete type. + pub fn downcast<T: Error + 'static>(self: Box<Self>) -> Result<Box<T>, Box<dyn Error + Send>> { + let err: Box<dyn Error> = self; + <dyn Error>::downcast(err).map_err(|s| unsafe { + // Reapply the `Send` marker. + mem::transmute::<Box<dyn Error>, Box<dyn Error + Send>>(s) + }) + } +} + +impl dyn Error + Send + Sync { + #[inline] + #[stable(feature = "error_downcast", since = "1.3.0")] + #[rustc_allow_incoherent_impl] + /// Attempts to downcast the box to a concrete type. + pub fn downcast<T: Error + 'static>(self: Box<Self>) -> Result<Box<T>, Box<Self>> { + let err: Box<dyn Error> = self; + <dyn Error>::downcast(err).map_err(|s| unsafe { + // Reapply the `Send + Sync` marker. + mem::transmute::<Box<dyn Error>, Box<dyn Error + Send + Sync>>(s) + }) + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "rust1", since = "1.0.0")] +impl<'a, E: Error + 'a> From<E> for Box<dyn Error + 'a> { + /// Converts a type of [`Error`] into a box of dyn [`Error`]. + /// + /// # Examples + /// + /// ``` + /// use std::error::Error; + /// use std::fmt; + /// use std::mem; + /// + /// #[derive(Debug)] + /// struct AnError; + /// + /// impl fmt::Display for AnError { + /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + /// write!(f, "An error") + /// } + /// } + /// + /// impl Error for AnError {} + /// + /// let an_error = AnError; + /// assert!(0 == mem::size_of_val(&an_error)); + /// let a_boxed_error = Box::<dyn Error>::from(an_error); + /// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error)) + /// ``` + fn from(err: E) -> Box<dyn Error + 'a> { + Box::new(err) + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "rust1", since = "1.0.0")] +impl<'a, E: Error + Send + Sync + 'a> From<E> for Box<dyn Error + Send + Sync + 'a> { + /// Converts a type of [`Error`] + [`Send`] + [`Sync`] into a box of + /// dyn [`Error`] + [`Send`] + [`Sync`]. + /// + /// # Examples + /// + /// ``` + /// use std::error::Error; + /// use std::fmt; + /// use std::mem; + /// + /// #[derive(Debug)] + /// struct AnError; + /// + /// impl fmt::Display for AnError { + /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + /// write!(f, "An error") + /// } + /// } + /// + /// impl Error for AnError {} + /// + /// unsafe impl Send for AnError {} + /// + /// unsafe impl Sync for AnError {} + /// + /// let an_error = AnError; + /// assert!(0 == mem::size_of_val(&an_error)); + /// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(an_error); + /// assert!( + /// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error)) + /// ``` + fn from(err: E) -> Box<dyn Error + Send + Sync + 'a> { + Box::new(err) + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "rust1", since = "1.0.0")] +impl From<String> for Box<dyn Error + Send + Sync> { + /// Converts a [`String`] into a box of dyn [`Error`] + [`Send`] + [`Sync`]. + /// + /// # Examples + /// + /// ``` + /// use std::error::Error; + /// use std::mem; + /// + /// let a_string_error = "a string error".to_string(); + /// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_string_error); + /// assert!( + /// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error)) + /// ``` + #[inline] + fn from(err: String) -> Box<dyn Error + Send + Sync> { + struct StringError(String); + + impl Error for StringError { + #[allow(deprecated)] + fn description(&self) -> &str { + &self.0 + } + } + + impl fmt::Display for StringError { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + fmt::Display::fmt(&self.0, f) + } + } + + // Purposefully skip printing "StringError(..)" + impl fmt::Debug for StringError { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + fmt::Debug::fmt(&self.0, f) + } + } + + Box::new(StringError(err)) + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "string_box_error", since = "1.6.0")] +impl From<String> for Box<dyn Error> { + /// Converts a [`String`] into a box of dyn [`Error`]. + /// + /// # Examples + /// + /// ``` + /// use std::error::Error; + /// use std::mem; + /// + /// let a_string_error = "a string error".to_string(); + /// let a_boxed_error = Box::<dyn Error>::from(a_string_error); + /// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error)) + /// ``` + fn from(str_err: String) -> Box<dyn Error> { + let err1: Box<dyn Error + Send + Sync> = From::from(str_err); + let err2: Box<dyn Error> = err1; + err2 + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "rust1", since = "1.0.0")] +impl<'a> From<&str> for Box<dyn Error + Send + Sync + 'a> { + /// Converts a [`str`] into a box of dyn [`Error`] + [`Send`] + [`Sync`]. + /// + /// [`str`]: prim@str + /// + /// # Examples + /// + /// ``` + /// use std::error::Error; + /// use std::mem; + /// + /// let a_str_error = "a str error"; + /// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_str_error); + /// assert!( + /// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error)) + /// ``` + #[inline] + fn from(err: &str) -> Box<dyn Error + Send + Sync + 'a> { + From::from(String::from(err)) + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "string_box_error", since = "1.6.0")] +impl From<&str> for Box<dyn Error> { + /// Converts a [`str`] into a box of dyn [`Error`]. + /// + /// [`str`]: prim@str + /// + /// # Examples + /// + /// ``` + /// use std::error::Error; + /// use std::mem; + /// + /// let a_str_error = "a str error"; + /// let a_boxed_error = Box::<dyn Error>::from(a_str_error); + /// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error)) + /// ``` + fn from(err: &str) -> Box<dyn Error> { + From::from(String::from(err)) + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "cow_box_error", since = "1.22.0")] +impl<'a, 'b> From<Cow<'b, str>> for Box<dyn Error + Send + Sync + 'a> { + /// Converts a [`Cow`] into a box of dyn [`Error`] + [`Send`] + [`Sync`]. + /// + /// # Examples + /// + /// ``` + /// use std::error::Error; + /// use std::mem; + /// use std::borrow::Cow; + /// + /// let a_cow_str_error = Cow::from("a str error"); + /// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_cow_str_error); + /// assert!( + /// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error)) + /// ``` + fn from(err: Cow<'b, str>) -> Box<dyn Error + Send + Sync + 'a> { + From::from(String::from(err)) + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "cow_box_error", since = "1.22.0")] +impl<'a> From<Cow<'a, str>> for Box<dyn Error> { + /// Converts a [`Cow`] into a box of dyn [`Error`]. + /// + /// # Examples + /// + /// ``` + /// use std::error::Error; + /// use std::mem; + /// use std::borrow::Cow; + /// + /// let a_cow_str_error = Cow::from("a str error"); + /// let a_boxed_error = Box::<dyn Error>::from(a_cow_str_error); + /// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error)) + /// ``` + fn from(err: Cow<'a, str>) -> Box<dyn Error> { + From::from(String::from(err)) + } +} + +#[stable(feature = "box_error", since = "1.8.0")] +impl<T: core::error::Error> core::error::Error for Box<T> { + #[allow(deprecated, deprecated_in_future)] + fn description(&self) -> &str { + core::error::Error::description(&**self) + } + + #[allow(deprecated)] + fn cause(&self) -> Option<&dyn core::error::Error> { + core::error::Error::cause(&**self) + } + + fn source(&self) -> Option<&(dyn core::error::Error + 'static)> { + core::error::Error::source(&**self) + } +} |