Struct TaggedPtr 

pub struct TaggedPtr<T, const BITS: usize>(/* private fields */);

A tagged pointer: a space-efficient representation of a pointer and integer tag.

This type stores a pointer and an integer tag without taking up more space than a normal pointer. Conceptually, this type behaves as if it contains a NonNull<T> and a certain number of bits of an integer tag.

BITS specifies how many bits are used for the tag. The alignment of T must be large enough to store this many bits: if BITS is larger than the base-2 logarithm of the alignment of T¹, panics or compilation errors will occur.

---

1. Because alignment is always a power of 2, this is equal to align_of::<T>().trailing_zeros(). ↩

Implementations

impl<T, const BITS: usize> TaggedPtr<T, BITS>

pub const BITS: u32

The number of tag bits that this tagged pointer can store.

pub const MAX_TAG: usize

The maximum tag (inclusive) that this tagged pointer can store. Equal to (1 << BITS) - 1 (i.e., one less than 2 to the power of BITS).

pub fn new(ptr: NonNull<T>, tag: usize) -> Self

Creates a new tagged pointer. Only the lower BITS bits of tag are stored.

Panics

ptr must be aligned to at least 2^BITS (i.e., 1 << BITS) or panics may occur. It is recommended that ptr be properly aligned for T, which automatically fulfills this requirement due to the restriction on BITS above.

pub unsafe fn new_unchecked(ptr: NonNull<T>, tag: usize) -> Self

Equivalent to Self::new but without some runtime checks.

Safety

• ptr must be aligned to at least 2^BITS (i.e., 1 << BITS).
• tag cannot be greater than Self::MAX_TAG.

pub unsafe fn new_unchecked_dereferenceable(ptr: NonNull<T>, tag: usize) -> Self

Like Self::new_unchecked, but the pointer must be dereferenceable, which allows better optimization.

Safety

All conditions of Self::new_unchecked must be upheld, plus at least the first 2^BITS (i.e., 1 << BITS) bytes of ptr must be “dereferenceable” in the sense defined by core::ptr.

impl<T, const BITS: usize> TaggedPtr<T, BITS>

pub fn get(self) -> (NonNull<T>, usize)

Gets the pointer and tag stored by the tagged pointer.

If you need both the pointer and tag, this method may be more efficient than calling Self::ptr and Self::tag separately.

pub fn ptr(self) -> NonNull<T>

Gets the pointer stored by the tagged pointer, without the tag. Equivalent to self.get().0.

pub fn set_ptr(&mut self, ptr: NonNull<T>)

Sets the pointer without modifying the tag.

This method is simply equivalent to:

*self = Self::new(ptr, self.tag());

See Self::new for information on argument validity and panics.

pub fn tag(self) -> usize

Gets the tag stored by the tagged pointer. Equivalent to self.get().1.

pub fn set_tag(&mut self, tag: usize)

Sets the tag without modifying the pointer.

This method is simply equivalent to:

*self = Self::new(self.ptr(), tag);

See Self::new for more information.

Trait Implementations

impl<T, const BITS: usize> Clone for TaggedPtr<T, BITS>

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<T, const BITS: usize> Debug for TaggedPtr<T, BITS>

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

Formats the value using the given formatter.

impl<T, const BITS: usize> Hash for TaggedPtr<T, BITS>

fn hash<H: Hasher>(&self, state: &mut H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl<T, const BITS: usize> Ord for TaggedPtr<T, BITS>

fn cmp(&self, other: &Self) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

impl<T, const BITS: usize> PartialEq for TaggedPtr<T, BITS>

fn eq(&self, other: &Self) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T, const BITS: usize> PartialOrd for TaggedPtr<T, BITS>

fn partial_cmp(&self, other: &Self) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

Tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

Tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl<T, const BITS: usize> Copy for TaggedPtr<T, BITS>

impl<T, const BITS: usize> Eq for TaggedPtr<T, BITS>