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Add unchecked downcast methods #90851

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merged 4 commits into from
Dec 4, 2021
Merged

Add unchecked downcast methods #90851

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29403ee
add unchecked downcast methods
ibraheemdev Nov 13, 2021
6f98293
add tracking issue for `downcast_unchecked`
ibraheemdev Nov 13, 2021
25271a5
fix doc links for `downcast_unchecked`
ibraheemdev Nov 20, 2021
4ec5cdc
fix stability annotations for `Box::downcast`
ibraheemdev Dec 3, 2021
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137 changes: 109 additions & 28 deletions library/alloc/src/boxed.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1482,8 +1482,6 @@ impl<T, const N: usize> TryFrom<Box<[T]>> for Box<[T; N]> {
}

impl<A: Allocator> Box<dyn Any, A> {
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
/// Attempt to downcast the box to a concrete type.
///
/// # Examples
Expand All @@ -1501,21 +1499,48 @@ impl<A: Allocator> Box<dyn Any, A> {
/// print_if_string(Box::new(my_string));
/// print_if_string(Box::new(0i8));
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn downcast<T: Any>(self) -> Result<Box<T, A>, Self> {
if self.is::<T>() {
unsafe {
let (raw, alloc): (*mut dyn Any, _) = Box::into_raw_with_allocator(self);
Ok(Box::from_raw_in(raw as *mut T, alloc))
}
} else {
Err(self)
if self.is::<T>() { unsafe { Ok(self.downcast_unchecked::<T>()) } } else { Err(self) }
}

/// Downcasts the box to a concrete type.
///
/// For a safe alternative see [`downcast`].
///
/// # Examples
///
/// ```
/// #![feature(downcast_unchecked)]
///
/// use std::any::Any;
///
/// let x: Box<dyn Any> = Box::new(1_usize);
///
/// unsafe {
/// assert_eq!(*x.downcast_unchecked::<usize>(), 1);
/// }
/// ```
///
/// # Safety
///
/// The contained value must be of type `T`. Calling this method
/// with the incorrect type is *undefined behavior*.
///
/// [`downcast`]: Self::downcast
#[inline]
#[unstable(feature = "downcast_unchecked", issue = "90850")]
pub unsafe fn downcast_unchecked<T: Any>(self) -> Box<T, A> {
debug_assert!(self.is::<T>());
unsafe {
let (raw, alloc): (*mut dyn Any, _) = Box::into_raw_with_allocator(self);
Box::from_raw_in(raw as *mut T, alloc)
}
}
}

impl<A: Allocator> Box<dyn Any + Send, A> {
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
/// Attempt to downcast the box to a concrete type.
///
/// # Examples
Expand All @@ -1533,21 +1558,48 @@ impl<A: Allocator> Box<dyn Any + Send, A> {
/// print_if_string(Box::new(my_string));
/// print_if_string(Box::new(0i8));
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn downcast<T: Any>(self) -> Result<Box<T, A>, Self> {
if self.is::<T>() {
unsafe {
let (raw, alloc): (*mut (dyn Any + Send), _) = Box::into_raw_with_allocator(self);
Ok(Box::from_raw_in(raw as *mut T, alloc))
}
} else {
Err(self)
if self.is::<T>() { unsafe { Ok(self.downcast_unchecked::<T>()) } } else { Err(self) }
}

/// Downcasts the box to a concrete type.
///
/// For a safe alternative see [`downcast`].
///
/// # Examples
///
/// ```
/// #![feature(downcast_unchecked)]
///
/// use std::any::Any;
///
/// let x: Box<dyn Any + Send> = Box::new(1_usize);
///
/// unsafe {
/// assert_eq!(*x.downcast_unchecked::<usize>(), 1);
/// }
/// ```
///
/// # Safety
///
/// The contained value must be of type `T`. Calling this method
/// with the incorrect type is *undefined behavior*.
///
/// [`downcast`]: Self::downcast
#[inline]
#[unstable(feature = "downcast_unchecked", issue = "90850")]
pub unsafe fn downcast_unchecked<T: Any>(self) -> Box<T, A> {
debug_assert!(self.is::<T>());
unsafe {
let (raw, alloc): (*mut (dyn Any + Send), _) = Box::into_raw_with_allocator(self);
Box::from_raw_in(raw as *mut T, alloc)
}
}
}

impl<A: Allocator> Box<dyn Any + Send + Sync, A> {
#[inline]
#[stable(feature = "box_send_sync_any_downcast", since = "1.51.0")]
/// Attempt to downcast the box to a concrete type.
///
/// # Examples
Expand All @@ -1565,15 +1617,44 @@ impl<A: Allocator> Box<dyn Any + Send + Sync, A> {
/// print_if_string(Box::new(my_string));
/// print_if_string(Box::new(0i8));
/// ```
#[inline]
#[stable(feature = "box_send_sync_any_downcast", since = "1.51.0")]
pub fn downcast<T: Any>(self) -> Result<Box<T, A>, Self> {
if self.is::<T>() {
unsafe {
let (raw, alloc): (*mut (dyn Any + Send + Sync), _) =
Box::into_raw_with_allocator(self);
Ok(Box::from_raw_in(raw as *mut T, alloc))
}
} else {
Err(self)
if self.is::<T>() { unsafe { Ok(self.downcast_unchecked::<T>()) } } else { Err(self) }
}

/// Downcasts the box to a concrete type.
///
/// For a safe alternative see [`downcast`].
///
/// # Examples
///
/// ```
/// #![feature(downcast_unchecked)]
///
/// use std::any::Any;
///
/// let x: Box<dyn Any + Send + Sync> = Box::new(1_usize);
///
/// unsafe {
/// assert_eq!(*x.downcast_unchecked::<usize>(), 1);
/// }
/// ```
///
/// # Safety
///
/// The contained value must be of type `T`. Calling this method
/// with the incorrect type is *undefined behavior*.
///
/// [`downcast`]: Self::downcast
#[inline]
#[unstable(feature = "downcast_unchecked", issue = "90850")]
pub unsafe fn downcast_unchecked<T: Any>(self) -> Box<T, A> {
debug_assert!(self.is::<T>());
unsafe {
let (raw, alloc): (*mut (dyn Any + Send + Sync), _) =
Box::into_raw_with_allocator(self);
Box::from_raw_in(raw as *mut T, alloc)
}
}
}
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