Struct tagged_pointer::TaggedPtr

#[repr(transparent)]
pub struct TaggedPtr<T, const BITS: usize>(_);

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 (unless the fallback implementation is used; see the crate documentation).

The tagged pointer conceptually holds 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; see Self::new.

Implementations

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

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

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

A check is performed at compile time to ensure that the alignment of T is not less than 2^BITS (1 << BITS). This ensures that all properly aligned pointers to T will be aligned enough to store the specified number of bits of the tag.

Panics

ptr should be “dereferenceable” in the sense defined by core::ptr.¹ If it is not, this function or methods of TaggedPtr may panic.

It is recommended that ptr be properly aligned (i.e., aligned to at least mem::align_of::<T>()), but it may have a smaller alignment. However, if its alignment is not at least 2^BITS, this function may panic.

---

1. It is permissible for only the first 2^BITS bytes of ptr to be dereferenceable. ↩

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.

Panics

If the pointer provided to Self::new wasn’t “dereferenceable”, this method may panic.

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

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

Panics

If the pointer provided to Self::new wasn’t “dereferenceable”, this method may panic.

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());

Panics

See Self::new.

pub fn tag(self) -> usize

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

Panics

If the pointer provided to Self::new wasn’t “dereferenceable”, this method may panic.

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);

Panics

See Self::new.

Trait Implementations

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

fn clone(&self) -> Self

Returns a copy 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) -> Selfwhere Self: Sized,

Compares and returns the maximum of two values.

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

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Selfwhere Self: Sized + PartialOrd<Self>,

Restrict a value to a certain interval.

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

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

This method tests for self and other values to be equal, and is used by ==.

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

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

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

This method tests less than (for self and other) and is used by the < operator.

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

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

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

This method tests greater than (for self and other) and is used by the > operator.

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

This method 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>