Ensure the last element of reduction in the throttle is emitted and use appropriate delay (#292)

Author: phausler

Sources/AsyncAlgorithms/AsyncThrottleSequence.swift

@@ -81,7 +81,16 @@ extension AsyncThrottleSequence: AsyncSequence {
 letstart= last ?? clock.now
 repeat{
 guardlet element =tryawait base.next()else{
-returnnil
+if reduced !=nil,let last {
+ // ensure the rate of elements never exceeds the given interval
+letamount= interval - last.duration(to: clock.now)
+if amount >.zero {
+try?await clock.sleep(for: amount)
+}
+}
+ // the last value is unable to have any subsequent
+ // values so always return the last reduction
+return reduced
 }
 letreduction=awaitreducing(reduced, element)
 letnow= clock.now

Tests/AsyncAlgorithmsTests/TestThrottle.swift

@@ -72,7 +72,7 @@ final class TestThrottle: XCTestCase {
 validate{
 "abcdefghijk|"
  $0.inputs[0].throttle(for:.steps(3), clock: $0.clock)
-"a--d--g--j-|"
+"a--d--g--j--[k|]"
 }
 }
 
@@ -81,7 +81,7 @@ final class TestThrottle: XCTestCase {
 validate{
 "abcdefghijk|"
  $0.inputs[0].throttle(for:.steps(3), clock: $0.clock, latest:false)
-"a--b--e--h-|"
+"a--b--e--h--[k|]"
 }
 }
 
@@ -138,4 +138,22 @@ final class TestThrottle: XCTestCase {
 "-a---c---e---g---i---k-|"
 }
 }
+
+func test_trailing_delay_without_latest()throws{
+guard #available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0,*)else{throwXCTSkip("Skipped due to Clock/Instant/Duration availability")}
+validate{
+"abcdefghijkl|"
+ $0.inputs[0].throttle(for:.steps(3), clock: $0.clock, latest:false)
+"a--b--e--h--[k|]"
+}
+}
+
+func test_trailing_delay_with_latest()throws{
+guard #available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0,*)else{throwXCTSkip("Skipped due to Clock/Instant/Duration availability")}
+validate{
+"abcdefghijkl|"
+ $0.inputs[0].throttle(for:.steps(3), clock: $0.clock, latest:true)
+"a--d--g--j--[l|]"
+}
+}
 }