pub struct SelfCell<O, D>where
O: StableDeref,{ /* private fields */ }
Expand description
A container carrying a derived object alongside its owner.
Warning: This is an inherently unsafe type that builds on top of StableDeref
and
AsSelf
to establish somewhat safe memory semantics. Always try to avoid self-references by
storing data in an outer scope or avoiding the need alltogether, first.
SelfCell
stores an owner object that must implement StableDeref
. This guarantees that the
reference pointed to by the dependent object never moves over the lifetime of this object. This
is already implemented for most heap-allocating types, like Box
, Rc
, Arc
or ByteView
.
Additionally, the dependent object must implement AsSelf
. This guarantees that the borrow’s
lifetime and its lifetime bounds never exceed the lifetime of the owner. As such, an object
Foo<'a>
that borrows data from the owner, will be coerced down to Foo<'self>
when borrowing.
There are two constructor functions, new
and try_new
, each of which are passed a pointer to
the owned data. Dereferencing this pointer is intentionally unsafe, and beware that a borrow of
that pointer must not leave the callback.
While it is possible to store derived references in a SelfCell
, too, there are simpler
alternatives, such as owning_ref::OwningRef
. Consider using such types before using
SelfCell
.
Example
use symbolic_common::{AsSelf, SelfCell};
struct Foo<'a>(&'a str);
impl<'slf> AsSelf<'slf> for Foo<'_> {
type Ref = Foo<'slf>;
fn as_self(&'slf self) -> &Self::Ref {
self
}
}
let owner = String::from("hello world");
let cell = SelfCell::new(owner, |s| Foo(unsafe { &*s }));
assert_eq!(cell.get().0, "hello world");
Implementations§
source§impl<'slf, O, T> SelfCell<O, T>where
O: StableDeref + 'slf,
T: AsSelf<'slf>,
impl<'slf, O, T> SelfCell<O, T>where O: StableDeref + 'slf, T: AsSelf<'slf>,
sourcepub fn new<F>(owner: O, derive: F) -> SelfCell<O, T>where
F: FnOnce(*const <O as Deref>::Target) -> T,
pub fn new<F>(owner: O, derive: F) -> SelfCell<O, T>where F: FnOnce(*const <O as Deref>::Target) -> T,
Creates a new SelfCell
.
Safety
The callback receives a pointer to the owned data. Dereferencing the pointer is unsafe. Note that a borrow to that data can only safely be used to derive the object and must not leave the callback.
Example
use symbolic_common::SelfCell;
let owner = String::from("hello world");
let cell = SelfCell::new(owner, |s| unsafe { &*s });
sourcepub fn try_new<E, F>(owner: O, derive: F) -> Result<SelfCell<O, T>, E>where
F: FnOnce(*const <O as Deref>::Target) -> Result<T, E>,
pub fn try_new<E, F>(owner: O, derive: F) -> Result<SelfCell<O, T>, E>where F: FnOnce(*const <O as Deref>::Target) -> Result<T, E>,
Creates a new SelfCell
which may fail to construct.
Safety
The callback receives a pointer to the owned data. Dereferencing the pointer is unsafe. Note that a borrow to that data can only safely be used to derive the object and must not leave the callback.
Example
use symbolic_common::SelfCell;
fn main() -> Result<(), std::str::Utf8Error> {
let owner = Vec::from("hello world");
let cell = SelfCell::try_new(owner, |s| unsafe { std::str::from_utf8(&*s) })?;
Ok(())
}
sourcepub unsafe fn from_raw(owner: O, derived: T) -> SelfCell<O, T>
pub unsafe fn from_raw(owner: O, derived: T) -> SelfCell<O, T>
Unsafely creates a new SelfCell
from a derived object by moving the owner.
Safety
This is an inherently unsafe process. The caller must guarantee that the derived object only borrows from the owner that is moved into this container and the borrowed reference has a stable address. This is useful, when cloning the owner by deriving a sub-object.
Example
use std::sync::Arc;
use symbolic_common::{AsSelf, SelfCell};
struct Foo<'a>(&'a str);
impl<'slf> AsSelf<'slf> for Foo<'_> {
type Ref = Foo<'slf>;
fn as_self(&'slf self) -> &Self::Ref {
self
}
}
// Create a clonable owner and move it into cell
let owner = Arc::<str>::from(" hello ");
let cell = SelfCell::new(owner, |s| Foo(unsafe { &*s }));
// Create a second derived object and clone the owner
let trimmed = Foo(cell.get().0.trim());
let cell2 = unsafe { SelfCell::from_raw(cell.owner().clone(), trimmed) };
// Now, drop the original cell and continue using the clone
assert_eq!(cell2.get().0, "hello");
Trait Implementations§
Auto Trait Implementations§
impl<O, D> RefUnwindSafe for SelfCell<O, D>where D: RefUnwindSafe, O: RefUnwindSafe,
impl<O, D> Send for SelfCell<O, D>where D: Send, O: Send,
impl<O, D> Sync for SelfCell<O, D>where D: Sync, O: Sync,
impl<O, D> Unpin for SelfCell<O, D>where D: Unpin, O: Unpin,
impl<O, D> UnwindSafe for SelfCell<O, D>where D: UnwindSafe, O: UnwindSafe,
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