Struct LookaheadBuf 

pub struct LookaheadBuf<T: Copy, const CAP: usize> { /* private fields */ }

Fixed-capacity ring buffer for parser lookahead.

Slots are MaybeUninit because the token type is expected to be Copy and the buffer tracks occupancy through head and len. Only head..head + len indices (modulo CAP) are considered initialised at any moment.

CAP must be a power of two; the indexing arithmetic uses a bitmask (& (CAP - 1)) instead of a modulo for speed. A debug-build assertion rejects non-power-of-two capacities during construction.

Implementations

impl<T: Copy, const CAP: usize> LookaheadBuf<T, CAP>

pub fn new() -> Self

Create an empty buffer. CAP must be a power of two; violating this in debug builds trips a panic on first use.

Panics

In debug builds, panics if CAP is not a power of two.

pub fn len(&self) -> usize

Number of tokens currently buffered.

pub fn is_empty(&self) -> bool

Whether the buffer is empty.

pub fn is_full(&self) -> bool

Whether the buffer is full. Callers that rely on the ring never overflowing (no expansion is possible) should check this before pushing.

pub const fn capacity(&self) -> usize

Capacity, identical to the CAP const generic.

pub fn push_back(&mut self, value: T)

Push a token at the back.

Hard-panics on overflow: the ring has no heap fallback and overwriting the oldest slot would silently corrupt the buffer. Callers must size CAP large enough for the deepest lookahead the parser ever performs.

Panics

Panics if CAP tokens have been pushed without any being consumed.

pub fn pop_front(&mut self) -> Option<T>

Pop the front token, or None if the buffer is empty.

pub fn get(&self, n: usize) -> Option<T>

Copy the nth-ahead token without consuming it (0 = next).

pub fn clear(&mut self)

Discard every buffered token. Leaves the ring ready for reuse.

Trait Implementations

impl<T: Copy, const CAP: usize> Debug for LookaheadBuf<T, CAP>

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

Formats the value using the given formatter.

impl<T: Copy, const CAP: usize> Default for LookaheadBuf<T, CAP>

fn default() -> Self

Returns the “default value” for a type.