feat(rx): add count operator (#160)

rx/observable-operator-count_test.go

@@ -0,0 +1,50 @@
+package rx_test
+
+import (
+	"context"
+
+	"github.com/fortytw2/leaktest"
+	. "github.com/onsi/ginkgo/v2" //nolint:revive // ginkgo ok
+	"github.com/snivilised/lorax/rx"
+)
+
+var _ = Describe("Observable operator", func() {
+	Context("Count", func() {
+		Context("principle", func() {
+			It("🧪 should: ", func() {
+				// rxgo: Test_Observable_Count
+				defer leaktest.Check(GinkgoT())()
+
+				ctx, cancel := context.WithCancel(context.Background())
+				defer cancel()
+
+				rx.Assert(ctx, rx.Range[int](1, 100).Count(),
+					rx.HasNumber[int]{
+						Expected: 100,
+					})
+			})
+		})
+
+		Context("Parallel", func() {
+			Context("given: foo", func() {
+				It("🧪 should: ", func() {
+					// rxgo: Test_Observable_Count_Parallel
+					defer leaktest.Check(GinkgoT())()
+
+					/*
+						ctx, cancel := context.WithCancel(context.Background())
+						defer cancel()
+
+						rx.Assert(ctx, rx.Range[int](1, 100).Count(
+							rx.WithCPUPool[int](),
+						),
+							rx.HasNumber[int]{
+								Expected: 100,
+							},
+						)
+					*/
+				})
+			})
+		})
+	})
+})

rx/observable-operator.go

@@ -270,6 +270,42 @@ func (op *containsOperator[T]) gatherNext(ctx context.Context, item Item[T],
 	}
 }
 
+func (o *ObservableImpl[T]) Count(opts ...Option[T]) Single[T] {
+	const (
+		forceSeq     = true
+		bypassGather = false
+	)
+
+	return single(o.parent, o, func() operator[T] {
+		return &countOperator[T]{}
+	}, forceSeq, bypassGather, opts...)
+}
+
+type countOperator[T any] struct {
+	count int
+}
+
+func (op *countOperator[T]) next(_ context.Context, _ Item[T],
+	_ chan<- Item[T], _ operatorOptions[T],
+) {
+	op.count++
+}
+
+func (op *countOperator[T]) err(_ context.Context, _ Item[T],
+	_ chan<- Item[T], operatorOptions operatorOptions[T],
+) {
+	operatorOptions.stop()
+}
+
+func (op *countOperator[T]) end(ctx context.Context, dst chan<- Item[T]) {
+	Num[T](op.count).SendContext(ctx, dst)
+}
+
+func (op *countOperator[T]) gatherNext(_ context.Context, _ Item[T],
+	_ chan<- Item[T], _ operatorOptions[T],
+) {
+}
+
 // Max determines and emits the maximum-valued item emitted by an Observable according to a comparator.
 func (o *ObservableImpl[T]) Max(comparator Comparator[T], initLimit InitLimit[T],
 	opts ...Option[T],

rx/observable.go

@@ -16,6 +16,7 @@ type Observable[T any] interface {
 	BackOffRetry(backOffCfg backoff.BackOff, opts ...Option[T]) Observable[T]
 	Connect(ctx context.Context) (context.Context, Disposable)
 	Contains(equal Predicate[T], opts ...Option[T]) Single[T]
+	Count(opts ...Option[T]) Single[T]
 
 	Max(comparator Comparator[T], initLimit InitLimit[T], opts ...Option[T]) OptionalSingle[T]
 	Map(apply Func[T], opts ...Option[T]) Observable[T]