Struct Handle 

pub struct Handle<T> { /* private fields */ }

An opaque, copyable reference to a value stored in a Region.

A handle wraps a slotmap::DefaultKey (an index plus a generation) and a region_id that identifies which Region instance the handle belongs to. It is Copy and unconditionally Send + Sync regardless of T — it owns no T, it only names one. The PhantomData<fn() -> T> keeps the handle typed (so a Handle<A> cannot be passed to a Region<B>) while staying covariant in T and free of any drop/auto-trait obligations.

The region_id: NonZeroUsize field ensures that handles from different Region instances never collide even if they have the same key. Using NonZeroUsize preserves the niche optimization for Option<Handle<T>>. region_id is pointer-width (not a fixed 64 bits) so this type stays buildable on no_std targets without 64-bit atomics (e.g. thumbv7em-none-eabi, i686-*) — every such target still has pointer-width atomics.

Layout is an observed property, not a guarantee

This crate does not use #[repr(C)]/#[repr(transparent)] here — there is no FFI or C-ABI use case for Handle<T>, and one would be misleading regardless: the inner slotmap::DefaultKey is itself not #[repr(C)] upstream, so pinning only the outer field order would not yield an actual stable C layout. size_of::<Handle<T>>() (16 bytes on a 64-bit host, 12 on 32-bit) and the Option<Handle<T>> niche optimization are current, observed properties of this implementation, verified by tests/handle_static_asserts.rs — a tripwire against silent drift (e.g. a future slotmap minor bump changing DefaultKey’s size), not a stable public contract. If a genuine FFI need arises, the crate would add an explicit to_raw/from_raw conversion pair rather than promise this struct’s layout.

Trait Implementations

impl<T> Clone for Handle<T>

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<T> Copy for Handle<T>

impl<T> Debug for Handle<T>

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

Formats the value using the given formatter.

impl<T> Eq for Handle<T>

impl<T> Hash for Handle<T>

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> Ord for Handle<T>

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> PartialEq for Handle<T>

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

Equality operator ==.

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

Inequality operator !=.

impl<T> PartialOrd for Handle<T>

Ord/PartialOrd provide a total order consistent with Eq, suitable for storing Handle<T> in a BTreeMap/BTreeSet or sorting a Vec of them. The relative order between two particular handles — including whether handles from different Regions group together or interleave — is an unspecified implementation detail (currently: group by region_id, tie-break by key) and may change in any release. Do not depend on it for anything beyond “a total order exists”.

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.