fetchLatestHeartRateSample.swift

public func fetchLatestHeartRateSample(
  completion: @escaping (_ sample: HKQuantitySample?) -> Void) {

  /// Create sample type for the heart rate
  guard let sampleType = HKObjectType
    .quantityType(forIdentifier: .heartRate) else {
      completion(nil)
    return
  }

  /// Predicate for specifiying start and end dates for the query
  let predicate = HKQuery
    .predicateForSamples(
      withStart: Date.distantPast,
      end: Date(),
      options: .strictEndDate)

  /// Set sorting by date.
  let sortDescriptor = NSSortDescriptor(
    key: HKSampleSortIdentifierStartDate,
    ascending: false)

  /// Create the query
  let query = HKSampleQuery(
    sampleType: sampleType,
    predicate: predicate,
    limit: Int(HKObjectQueryNoLimit),
    sortDescriptors: [sortDescriptor]) { (_, results, error) in

      guard error == nil else {
        print("Error: \(error!.localizedDescription)")
        return
      }
      
      completion(results?[0] as? HKQuantitySample)
  }

  self.healthStore.execute(query)
}