threshold specification

This is the engineering specification for the MotionObservable operator: threshold.

Overview

threshold emits a ThresholdEvent based on the incoming value’s position around a threshold.

Example usage

stream.threshold(50)

upstream position  |  downstream
20       50        |  .below
50       50        |  .within
60       50        |  .above

MVP

Expose a ThresholdSide enum type

public enum ThresholdSide {
  case below
  case within
  case above
}

Expose a threshold operator API

Use _nextOperator to implement the operator. Accept a single position value.

class MotionObservable<number> {
  public func threshold<U>(_ threshold: number) -> MotionObservable<ThresholdSide>