Struct WindowedIterState 

pub struct WindowedIterState<I, T> {
    len: usize,
    iter: RefCell<Option<I>>,
    consumed: RefCell<usize>,
    window: RefCell<Vec<T>>,
    window_start: RefCell<usize>,
    window_size: usize,
    materialized: OnceLock<Vec<T>>,
}

Core state for windowed iterator-backed ALTREP vectors.

Like super::IterState, but only keeps a sliding window of elements in memory. Access within the window is O(1), and reading past it slides the window forward. The iterator cannot be rewound, so reading an element that has left the window is an error. Use super::IterState when R may read elements again or out of order.

This is useful for large iterators where only a small region is accessed at a time (e.g., streaming data processed in order).

Type Parameters

• I: The iterator type
• T: The element type produced by the iterator

Fields

len: usize

iter: RefCell<Option<I>>

consumed: RefCell<usize>

window: RefCell<Vec<T>>

window_start: RefCell<usize>

window_size: usize

materialized: OnceLock<Vec<T>>

Implementations

impl<I, T> WindowedIterState<I, T>

where I: Iterator<Item = T>, T: Copy,

pub fn new(iter: I, len: usize, window_size: usize) -> Self

Create a new windowed iterator state.

pub fn get_element(&self, i: usize) -> Option<T>

Get element at index i.

fn advance_to(&self, i: usize)

Advance the iterator to fill a window containing index i.

pub fn materialize_all(&self) -> &[T]

Materialize all elements.

Panics

If elements have already left the window, or if the iterator ends before the declared length.

pub fn as_materialized(&self) -> Option<&[T]>

Get materialized slice if available.

pub fn len(&self) -> usize

Get the length.

pub fn is_empty(&self) -> bool

Check if empty.

impl<I, T> WindowedIterState<I, T>

where I: ExactSizeIterator<Item = T>, T: Copy,

pub fn from_exact_size(iter: I, window_size: usize) -> Self

Create from an ExactSizeIterator.

Layout

Note: Unable to compute type layout, possibly due to this type having generic parameters. Layout can only be computed for concrete, fully-instantiated types.