struct Cursor<D: Data> {
chunks: VecDeque<Rc<Chunk<D>>>,
chunk_offset: usize,
limit: Option<usize>,
overwrite_ts: Option<Timestamp>,
}
Expand description
A cursor over updates in a chain.
A cursor provides two guarantees:
- Produced updates are ordered and consolidated.
- A cursor always yields at least one update.
The second guarantee is enforced through the type system: Every method that steps a cursor
forward consumes self
and returns an Option<Cursor>
that’s None
if the operation stepped
over the last update.
A cursor holds on to Rc<Chunk>
s, allowing multiple cursors to produce updates from the same
chunks concurrently. As soon as a cursor is done producing updates from a Chunk
it drops
its reference. Once the last cursor is done with a Chunk
its memory can be reclaimed.
Fields§
§chunks: VecDeque<Rc<Chunk<D>>>
The chunks from which updates can still be produced.
chunk_offset: usize
The current offset into chunks.front()
.
limit: Option<usize>
An optional limit for the number of updates the cursor will produce.
overwrite_ts: Option<Timestamp>
An optional overwrite for the timestamp of produced updates.
Implementations§
Source§impl<D: Data> Cursor<D>
impl<D: Data> Cursor<D>
Sourcefn new(chunks: VecDeque<Rc<Chunk<D>>>) -> Option<Self>
fn new(chunks: VecDeque<Rc<Chunk<D>>>) -> Option<Self>
Construct a cursor over a list of chunks.
Returns None
if chunks
is empty.
Sourcefn set_limit(self, limit: usize) -> Option<Self>
fn set_limit(self, limit: usize) -> Option<Self>
Set a limit for the number of updates this cursor will produce.
§Panics
Panics if there is already a limit lower than the new one.
Sourcefn step(self) -> Option<Self>
fn step(self) -> Option<Self>
Step to the next update.
Returns the stepped cursor, or None
if the step was over the last update.
Sourcefn skip_chunk(self) -> Option<(Self, usize)>
fn skip_chunk(self) -> Option<(Self, usize)>
Skip the remainder of the current chunk.
Returns the forwarded cursor and the number of updates skipped, or None
if no chunks are
left after the skip.
Sourcefn skip_time(self, time: Timestamp) -> Option<(Self, usize)>
fn skip_time(self, time: Timestamp) -> Option<(Self, usize)>
Skip all updates with times <= the given time.
Returns the forwarded cursor and the number of updates skipped, or None
if no updates are
left after the skip.
Sourcefn advance_by(self, since_ts: Timestamp) -> Vec<Self>
fn advance_by(self, since_ts: Timestamp) -> Vec<Self>
Advance all updates in this cursor by the given since_ts
.
Returns a list of cursors, each of which yields ordered and consolidated updates that have
been advanced by since_ts
.
Sourcefn split_at_time(self, time: Timestamp) -> (Option<Self>, Option<Self>)
fn split_at_time(self, time: Timestamp) -> (Option<Self>, Option<Self>)
Split the cursor at the given time.
Returns two cursors, the first yielding all updates at times < time
, the second yielding
all updates at times >= time
. Both can be None
if they would be empty.
Sourcefn try_unwrap(self) -> Result<Chain<D>, (&'static str, Self)>
fn try_unwrap(self) -> Result<Chain<D>, (&'static str, Self)>
Attempt to unwrap the cursor into a Chain
.
This operation efficiently reuses chunks by directly inserting them into the output chain where possible.
An unwrap is only successful if the cursor’s limit
and overwrite_ts
are both None
and
the cursor has unique references to its chunks. If the unwrap fails, this method returns an
Err
containing the cursor in an unchanged state, allowing the caller to convert it into a
chain by copying chunks rather than reusing them.
Trait Implementations§
Auto Trait Implementations§
impl<D> Freeze for Cursor<D>
impl<D> RefUnwindSafe for Cursor<D>
impl<D> !Send for Cursor<D>
impl<D> !Sync for Cursor<D>
impl<D> Unpin for Cursor<D>
impl<D> UnwindSafe for Cursor<D>
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