Struct NodeId 

pub struct NodeId { /* private fields */ }

Generational node identifier with overflow protection.

NodeId provides a type-safe, generational index into the NodeArena. The generation counter ensures that stale references (to deleted nodes) are detected and rejected.

Memory Layout

NodeId (12 bytes on 64-bit systems):
┌──────────────────────────────────────────┐
│ index: u32      │ generation: u64        │
│ (4 bytes)       │ (8 bytes)              │
└──────────────────────────────────────────┘

Generational Index Pattern

When a node is removed from the arena, the slot’s generation is incremented. Any NodeId holding the old generation will fail validation when used for lookup.

Time 0: Allocate slot 5, generation 1 → NodeId { index: 5, generation: 1 }
Time 1: Remove slot 5 → slot generation becomes 2
Time 2: Lookup with NodeId { index: 5, generation: 1 } → FAILS (1 ≠ 2)
Time 3: Allocate slot 5, generation 2 → NodeId { index: 5, generation: 2 }
Time 4: Lookup with NodeId { index: 5, generation: 2 } → SUCCEEDS

Implementations

impl NodeId

pub const INVALID: NodeId

Invalid sentinel value used to represent “no node”.

Uses u32::MAX as index which is reserved and never allocated.

pub const MAX_GENERATION: u64

Maximum safe generation value before overflow protection kicks in.

Set to u64::MAX / 2 (~9.2 quintillion) to provide a safety margin. This allows for detection before actual overflow occurs.

pub const fn new(index: u32, generation: u64) -> Self

Creates a new NodeId with the given index and generation.

Arguments

• index - The slot index in the arena
• generation - The generation counter for this slot

Example

let id = NodeId::new(0, 1);
assert_eq!(id.index(), 0);
assert_eq!(id.generation(), 1);

pub const fn index(self) -> u32

Returns the slot index.

pub const fn generation(self) -> u64

Returns the generation counter.

pub const fn is_invalid(self) -> bool

Checks if this is the invalid sentinel value.

Example

assert!(NodeId::INVALID.is_invalid());
assert!(!NodeId::new(0, 1).is_invalid());

pub const fn is_valid(self) -> bool

Checks if this is a valid (non-sentinel) ID.

Note: This only checks the sentinel value, not whether the ID actually refers to a live node in an arena.

pub fn try_increment_generation(self) -> Result<u64, GenerationOverflowError>

Attempts to increment the generation, returning an error if overflow would occur.

This is used by NodeArena when a slot is freed and will be reused.

Errors

Returns GenerationOverflowError if the generation would exceed MAX_GENERATION.

Example

let id = NodeId::new(5, 1);
let next_gen = id.try_increment_generation()?;
assert_eq!(next_gen, 2);

pub const fn is_near_overflow(self) -> bool

Checks if the generation is approaching the overflow limit.

Returns true if generation is within 1000 of MAX_GENERATION. This can be used for proactive warnings.

Trait Implementations

impl Clone for NodeId

fn clone(&self) -> NodeId

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for NodeId

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

Formats the value using the given formatter.

impl Default for NodeId

fn default() -> Self

Returns NodeId::INVALID as the default value.

impl<'de> Deserialize<'de> for NodeId

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Display for NodeId

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

Formats the value using the given formatter.

impl Hash for NodeId

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 Ord for NodeId

fn cmp(&self, other: &NodeId) -> 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 PartialEq for NodeId

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 PartialOrd for NodeId

fn partial_cmp(&self, other: &NodeId) -> 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 Serialize for NodeId

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl Copy for NodeId

impl Eq for NodeId