Struct Unique

#[repr(transparent)]
#[doc(hidden)] pub struct Unique<T: ?Sized> {
    pointer: NonNull<T>,
    _marker: PhantomData<T>,
}

🔬This is a nightly-only experimental API. (ptr_internals)

A wrapper around a raw non-null *mut T that indicates that the possessor of this wrapper owns the referent. Useful for building abstractions like Box<T>, Vec<T>, String, and HashMap<K, V>.

Unlike *mut T, Unique<T> behaves “as if” it were an instance of T. It implements Send/Sync if T is Send/Sync. It also implies the kind of strong aliasing guarantees an instance of T can expect: the referent of the pointer should not be modified without a unique path to its owning Unique.

If you’re uncertain of whether it’s correct to use Unique for your purposes, consider using NonNull, which has weaker semantics.

Unlike *mut T, the pointer must always be non-null, even if the pointer is never dereferenced. This is so that enums may use this forbidden value as a discriminant – Option<Unique<T>> has the same size as Unique<T>. However the pointer may still dangle if it isn’t dereferenced.

Unlike *mut T, Unique<T> is covariant over T. This should always be correct for any type which upholds Unique’s aliasing requirements.

Fields

pointer: NonNull<T>

🔬This is a nightly-only experimental API. (ptr_internals)

_marker: PhantomData<T>

🔬This is a nightly-only experimental API. (ptr_internals)

Implementations

impl<T: Sized> Unique<T>

pub const fn dangling() -> Self

🔬This is a nightly-only experimental API. (ptr_internals)

Creates a new Unique that is dangling, but well-aligned.

This is useful for initializing types which lazily allocate, like Vec::new does.

Note that the pointer value may potentially represent a valid pointer to a T, which means this must not be used as a “not yet initialized” sentinel value. Types that lazily allocate must track initialization by some other means.

impl<T: ?Sized> Unique<T>

pub const unsafe fn new_unchecked(ptr: *mut T) -> Self

🔬This is a nightly-only experimental API. (ptr_internals)

Creates a new Unique.

Safety

ptr must be non-null.

pub const fn new(ptr: *mut T) -> Option<Self>

🔬This is a nightly-only experimental API. (ptr_internals)

Creates a new Unique if ptr is non-null.

pub const fn from_non_null(pointer: NonNull<T>) -> Self

🔬This is a nightly-only experimental API. (ptr_internals)

Create a new Unique from a NonNull in const context.

pub const fn as_ptr(self) -> *mut T

🔬This is a nightly-only experimental API. (ptr_internals)

Acquires the underlying *mut pointer.

pub const fn as_non_null_ptr(self) -> NonNull<T>

🔬This is a nightly-only experimental API. (ptr_internals)

Acquires the underlying *mut pointer.

pub const unsafe fn as_ref(&self) -> &T

🔬This is a nightly-only experimental API. (ptr_internals)

Dereferences the content.

The resulting lifetime is bound to self so this behaves “as if” it were actually an instance of T that is getting borrowed. If a longer (unbound) lifetime is needed, use &*my_ptr.as_ptr().

pub const unsafe fn as_mut(&mut self) -> &mut T

🔬This is a nightly-only experimental API. (ptr_internals)

Mutably dereferences the content.

The resulting lifetime is bound to self so this behaves “as if” it were actually an instance of T that is getting borrowed. If a longer (unbound) lifetime is needed, use &mut *my_ptr.as_ptr().

pub const fn cast<U>(self) -> Unique<U>

🔬This is a nightly-only experimental API. (ptr_internals)

Casts to a pointer of another type.

Trait Implementations

impl<T: ?Sized> Clone for Unique<T>

fn clone(&self) -> Self

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T: ?Sized> Debug for Unique<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T: ?Sized> From<&mut T> for Unique<T>

fn from(reference: &mut T) -> Self

Converts a &mut T to a Unique<T>.

This conversion is infallible since references cannot be null.

impl<T: ?Sized> From<NonNull<T>> for Unique<T>

fn from(pointer: NonNull<T>) -> Self

Converts a NonNull<T> to a Unique<T>.

This conversion is infallible since NonNull cannot be null.

impl<T: ?Sized> From<Unique<T>> for NonNull<T>

fn from(unique: Unique<T>) -> Self

Converts to this type from the input type.

impl<T: ?Sized> Pointer for Unique<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T, U: ?Sized> CoerceUnsized<Unique<U>> for Unique<T>

where T: Unsize<U> + ?Sized,

impl<T: ?Sized> Copy for Unique<T>

impl<T, U: ?Sized> DispatchFromDyn<Unique<U>> for Unique<T>

where T: Unsize<U> + ?Sized,

impl<T: ?Sized> PinCoerceUnsized for Unique<T>

impl<T: Send + ?Sized> Send for Unique<T>

Unique pointers are Send if T is Send because the data they reference is unaliased. Note that this aliasing invariant is unenforced by the type system; the abstraction using the Unique must enforce it.

impl<T: Sync + ?Sized> Sync for Unique<T>

Unique pointers are Sync if T is Sync because the data they reference is unaliased. Note that this aliasing invariant is unenforced by the type system; the abstraction using the Unique must enforce it.

impl<T: UnwindSafe + ?Sized> UnwindSafe for Unique<T>