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//! Accumulator module contains the trait definition for aggregation function's accumulators.
use ArrayRef;
use ;
use Debug;
/// An accumulator represents a stateful object that lives throughout the evaluation of multiple rows and
/// generically accumulates values.
///
/// An accumulator knows how to:
/// * update its state from inputs via `update_batch`
/// * retract an update to its state from given inputs via `retract_batch`
/// * convert its internal state to a vector of aggregate values
/// * update its state from multiple accumulators' states via `merge_batch`
/// * compute the final value from its internal state via `evaluate`