Struct TailSeqMut 

pub struct TailSeqMut<'a, T: SeqElement> { /* private fields */ }

Streaming write cursor over a Seq<T> tail region.

Encodes/decodes ONE element at a time directly over the account bytes; push is O(1) (write one element at the tail, bump the count). The capacity is derived from the LIVE region length, so a tail that was grown via realloc can hold more elements with no type change. push returns AccountDataTooSmall when the region is full, grow the account first.

Implementations

impl<'a, T: SeqElement> TailSeqMut<'a, T>

pub fn from_region(region: &'a mut [u8]) -> Result<Self, ProgramError>

Overlay a write cursor on region (the tail bytes starting at the count prefix). Rejects a region too small for the prefix, or a stored count exceeding the region’s capacity (corrupt tail).

pub fn len(&self) -> u32

Number of live elements (the u32 count prefix).

pub fn is_empty(&self) -> bool

Whether the sequence is empty.

pub fn capacity(&self) -> usize

Live element capacity from the region length: (len - 4) / STRIDE.

pub fn is_full(&self) -> bool

Whether the sequence has reached its live capacity.

pub fn remaining_capacity(&self) -> usize

Remaining element slots before a grow is required.

pub fn get(&self, index: usize) -> Result<T, ProgramError>

Decode the element at index (one element, no full-tail decode).

pub fn set(&mut self, index: usize, value: T) -> Result<(), ProgramError>

Overwrite the element at index in place. index must be < len.

pub fn push(&mut self, value: T) -> Result<(), ProgramError>

Append value at the tail and bump the count, O(1). Returns AccountDataTooSmall when the region is at capacity (grow the account, then push again).

pub fn swap_remove(&mut self, index: usize) -> Result<T, ProgramError>

Remove the element at index, moving the last element into its slot (O(1), does not preserve order). Returns the removed value.

pub fn as_seq(&self) -> TailSeq<'_, T>

Borrow this cursor as a read cursor (shared reborrow).