Overhaul of stream.Stream function signature

internal/kvstore/kvstore.go

@@ -12,8 +12,8 @@ type Store[K, V any] interface {
 	Size() int
 	Get(key K) opt.Optional[V]
 	Put(key K, value V)
-	ForEach(func(key K, value V) bool) bool
-	ForEachKey(func(key K) bool) bool
+	ForEach(func(key K, value V) bool)
+	ForEachKey(func(key K) bool)
 }
 
 // NewMapped creates a new Store backed by a map.
@@ -66,22 +66,20 @@ func (s mappedStore[K, V]) Put(key K, value V) {
 	s[key] = value
 }
 
-func (s mappedStore[K, V]) ForEach(yield func(K, V) bool) bool {
+func (s mappedStore[K, V]) ForEach(yield func(K, V) bool) {
 	for k, v := range s {
 		if !yield(k, v) {
-			return false
+			break
 		}
 	}
-	return true
 }
 
-func (s mappedStore[K, V]) ForEachKey(yield func(K) bool) bool {
+func (s mappedStore[K, V]) ForEachKey(yield func(K) bool) {
 	for k := range s {
 		if !yield(k) {
-			return false
+			break
 		}
 	}
-	return true
 }
 
 // sortedStore provides an implementation of Store using sorted slices and binary-search.
@@ -121,20 +119,18 @@ func (s *sortedStore[K, V]) indexOf(key K) (int, bool) {
 	return slices.BinarySearchFunc(s.keys, key, s.compare)
 }
 
-func (s *sortedStore[K, V]) ForEach(yield func(K, V) bool) bool {
+func (s *sortedStore[K, V]) ForEach(yield func(K, V) bool) {
 	for i, k := range s.keys {
 		if !yield(k, s.values[i]) {
-			return false
+			break
 		}
 	}
-	return true
 }
 
-func (s *sortedStore[K, V]) ForEachKey(yield func(K) bool) bool {
+func (s *sortedStore[K, V]) ForEachKey(yield func(K) bool) {
 	for _, k := range s.keys {
 		if !yield(k) {
-			return false
+			break
 		}
 	}
-	return true
 }

pkg/opt/none.go

@@ -42,6 +42,10 @@ func (n None[V]) IfPresentElse(_ func(V), f func()) bool {
 	return false
 }
 
+func (n None[V]) Tap(_ func(V)) Optional[V] {
+	return n
+}
+
 func (n None[V]) String() string {
 	return "None"
 }

pkg/opt/optional.go

@@ -34,6 +34,10 @@ type Optional[V any] interface {
 	// Filter returns an Optional containing the value contained in the Optional if the provided predicate returns true for that value.
 	// If the Optional is empty, an empty Optional is returned.
 	Filter(func(V) bool) Optional[V]
+
+	// Tap calls the provided function with the value contained in the Optional if the Optional is not empty.
+	// Returns the Optional itself for chaining.
+	Tap(func(V)) Optional[V]
 }
 
 // Empty returns an empty Optional (None).

pkg/opt/optional_test.go

@@ -311,6 +311,36 @@ func TestIfPresentElse(t *testing.T) {
 	})
 }
 
+func TestTap(t *testing.T) {
+	t.Run("Some", func(t *testing.T) {
+		var called bool
+		o := Of(42)
+		o2 := o.Tap(func(i int) {
+			called = true
+		})
+		if o != o2 {
+			t.Errorf("expected Tap to return the Optional")
+		}
+		if !called {
+			t.Errorf("expected callback to be called")
+		}
+	})
+
+	t.Run("None", func(t *testing.T) {
+		var called bool
+		o := Empty[int]()
+		o2 := o.Tap(func(i int) {
+			called = true
+		})
+		if o != o2 {
+			t.Errorf("expected Tap to return the Optional")
+		}
+		if called {
+			t.Errorf("expected callback to not be called")
+		}
+	})
+}
+
 func TestString(t *testing.T) {
 	t.Run("Some", func(t *testing.T) {
 		o := Of(42)

pkg/opt/some.go

@@ -47,6 +47,11 @@ func (s Some[V]) IfPresentElse(f func(V), _ func()) bool {
 	return true
 }
 
+func (s Some[V]) Tap(f func(V)) Optional[V] {
+	f(s.Value)
+	return s
+}
+
 func (s Some[V]) String() string {
 	return fmt.Sprintf("Some(%#v)", s.Value)
 }

pkg/ptr/pointer_test.go

@@ -14,6 +14,7 @@ func TestRef(t *testing.T) {
 	p := Ref(i)
 	if p == nil {
 		t.Errorf("Ref(%v) = %v; want non-nil", i, p)
+		return
 	}
 	if *p != i {
 		t.Errorf("Ref(%v) = %v; want %v", i, p, i)

pkg/stream/combine.go

@@ -54,7 +54,7 @@ type OptionalCombiner[E1, E2, F any] func(E1, E2) opt.Optional[F]
 //	)
 //	out := stream.DebugString(s) // "<foo1>"
 func CombineOrDiscard[E1, E2, F any](s1 Stream[E1], s2 Stream[E2], combine OptionalCombiner[E1, E2, F]) Stream[F] {
-	return func(yield Consumer[F]) bool {
+	return func(yield Consumer[F]) {
 		ctx, cancel := context.WithCancel(context.Background())
 		defer cancel()
 
@@ -65,12 +65,12 @@ func CombineOrDiscard[E1, E2, F any](s1 Stream[E1], s2 Stream[E2], combine Optio
 			e1, ok1 := <-ch1
 			e2, ok2 := <-ch2
 			if !ok1 || !ok2 {
-				return true
+				return
 			}
 
 			if o := combine(e1, e2); o.Present() {
 				if !yield(o.GetOrZero()) {
-					return false
+					return
 				}
 			}
 		}

pkg/stream/filter.go

@@ -20,8 +20,8 @@ type Predicate[E any] func(e E) (pass bool)
 //	})
 //	out := stream.DebugString(s) // "<2>"
 func Filter[E any](s Stream[E], p Predicate[E]) Stream[E] {
-	return func(yield Consumer[E]) bool {
-		return s(func(e E) bool {
+	return func(yield Consumer[E]) {
+		s(func(e E) bool {
 			if p(e) {
 				return yield(e)
 			}
@@ -39,9 +39,9 @@ func Filter[E any](s Stream[E], p Predicate[E]) Stream[E] {
 //	})
 //	out := stream.DebugString(s) // "<(1, 2), (3, 4)>"
 func FilterIndexed[E any](s Stream[E], p func(E) bool) Stream[pair.Pair[int64, E]] {
-	return func(yield Consumer[pair.Pair[int64, E]]) bool {
+	return func(yield Consumer[pair.Pair[int64, E]]) {
 		var i int64
-		return s(func(e E) bool {
+		s(func(e E) bool {
 			i++
 			if p(e) {
 				return yield(pair.Of(i-1, e))
@@ -59,12 +59,12 @@ func FilterIndexed[E any](s Stream[E], p func(E) bool) Stream[pair.Pair[int64, E
 //	s := stream.Limit(stream.Of(1, 2, 3), 2)
 //	out := stream.DebugString(s) // "<1, 2>"
 func Limit[E any](s Stream[E], n int64) Stream[E] {
-	return func(yield Consumer[E]) bool {
+	return func(yield Consumer[E]) {
 		n := n // Shadow with a copy.
 		if n <= 0 {
-			return true
+			return // Nothing to do.
 		}
-		return s(func(e E) bool {
+		s(func(e E) bool {
 			n--
 			return yield(e) && n > 0
 		})
@@ -79,9 +79,9 @@ func Limit[E any](s Stream[E], n int64) Stream[E] {
 //	s := stream.Skip(stream.Of(1, 2, 3), 2)
 //	out := stream.DebugString(s) // "<3>"
 func Skip[E any](s Stream[E], n int64) Stream[E] {
-	return func(yield Consumer[E]) bool {
+	return func(yield Consumer[E]) {
 		n := n // Shadow with a copy.
-		return s(func(e E) bool {
+		s(func(e E) bool {
 			if n > 0 {
 				n--
 				return true
@@ -124,9 +124,9 @@ func DistinctBy[E any](s Stream[E], compare cmp.Comparer[E]) Stream[E] {
 }
 
 func distinct[E any](s Stream[E], kv kvstore.Maker[E, struct{}]) Stream[E] {
-	return func(yield Consumer[E]) bool {
+	return func(yield Consumer[E]) {
 		seen := kv()
-		return s(func(e E) bool {
+		s(func(e E) bool {
 			if seen.Get(e).Present() {
 				return true // Skip.
 			}

pkg/stream/from.go

@@ -14,13 +14,12 @@ import (
 //	s := stream.FromSlice([]int{1, 2, 3})
 //	out := stream.DebugString(s) // "<1, 2, 3>"
 func FromSlice[E any](s []E) Stream[E] {
-	return func(yield Consumer[E]) bool {
+	return func(yield Consumer[E]) {
 		for _, e := range s {
 			if !yield(e) {
-				return false // Consumer saw enough.
+				break // Consumer saw enough.
 			}
 		}
-		return true
 	}
 }
 
@@ -32,13 +31,12 @@ func FromSlice[E any](s []E) Stream[E] {
 //	s := stream.FromSliceBackwards([]int{1, 2, 3})
 //	out := stream.DebugString(s) // "<3, 2, 1>"
 func FromSliceBackwards[E any](s []E) Stream[E] {
-	return func(yield Consumer[E]) bool {
+	return func(yield Consumer[E]) {
 		for i := len(s) - 1; i >= 0; i-- {
 			if !yield(s[i]) {
-				return false // Consumer saw enough.
+				break // Consumer saw enough.
 			}
 		}
-		return true
 	}
 }
 
@@ -51,13 +49,12 @@ func FromSliceBackwards[E any](s []E) Stream[E] {
 //	s := stream.FromSliceWithIndex([]int{1, 2, 3})
 //	out := stream.DebugString(s) // "<(0, 1), (1, 2), (2, 3)>"
 func FromSliceWithIndex[E any](s []E) Stream[pair.Pair[int, E]] {
-	return func(yield Consumer[pair.Pair[int, E]]) bool {
+	return func(yield Consumer[pair.Pair[int, E]]) {
 		for i, e := range s {
 			if !yield(pair.Of(i, e)) {
-				return false // Consumer saw enough.
+				break // Consumer saw enough.
 			}
 		}
-		return true
 	}
 }
 
@@ -70,13 +67,12 @@ func FromSliceWithIndex[E any](s []E) Stream[pair.Pair[int, E]] {
 //	s := stream.FromSliceWithIndexBackwards([]int{1, 2, 3})
 //	out := stream.DebugString(s) // "<(2, 3), (1, 2), (0, 1)>"
 func FromSliceWithIndexBackwards[E any](s []E) Stream[pair.Pair[int, E]] {
-	return func(yield Consumer[pair.Pair[int, E]]) bool {
+	return func(yield Consumer[pair.Pair[int, E]]) {
 		for i := len(s) - 1; i >= 0; i-- {
 			if !yield(pair.Of(i, s[i])) {
-				return false // Consumer saw enough.
+				break // Consumer saw enough.
 			}
 		}
-		return true
 	}
 }
 
@@ -89,13 +85,12 @@ func FromSliceWithIndexBackwards[E any](s []E) Stream[pair.Pair[int, E]] {
 //	s := stream.FromMap(map[int]string{1: "foo", 2: "bar"})
 //	out := stream.DebugString(s) // "<(1, foo), (2, bar)>"
 func FromMap[K comparable, V any](m map[K]V) Stream[pair.Pair[K, V]] {
-	return func(yield Consumer[pair.Pair[K, V]]) bool {
+	return func(yield Consumer[pair.Pair[K, V]]) {
 		for k, v := range m {
 			if !yield(pair.Of(k, v)) {
-				return false // Consumer saw enough.
+				break // Consumer saw enough.
 			}
 		}
-		return true
 	}
 }
 
@@ -107,13 +102,12 @@ func FromMap[K comparable, V any](m map[K]V) Stream[pair.Pair[K, V]] {
 //	s := stream.FromMapKeys(map[int]string{1: "foo", 2: "bar"})
 //	out := stream.DebugString(s) // "<1, 2>" // Order not guaranteed.
 func FromMapKeys[K comparable, V any](m map[K]V) Stream[K] {
-	return func(yield Consumer[K]) bool {
+	return func(yield Consumer[K]) {
 		for k := range m {
 			if !yield(k) {
-				return false // Consumer saw enough.
+				break // Consumer saw enough.
 			}
 		}
-		return true
 	}
 }
 
@@ -125,13 +119,12 @@ func FromMapKeys[K comparable, V any](m map[K]V) Stream[K] {
 //	s := stream.FromMapValues(map[int]string{1: "foo", 2: "bar"})
 //	out := stream.DebugString(s) // "<foo, bar>" // Order not guaranteed.
 func FromMapValues[K comparable, V any](m map[K]V) Stream[V] {
-	return func(yield Consumer[V]) bool {
+	return func(yield Consumer[V]) {
 		for _, v := range m {
 			if !yield(v) {
-				return false
+				break // Consumer saw enough.
 			}
 		}
-		return true
 	}
 }
 
@@ -151,13 +144,12 @@ func FromMapValues[K comparable, V any](m map[K]V) Stream[V] {
 //	s := stream.FromChannel(ch)
 //	out := stream.DebugString(s) // "<1, 2>"
 func FromChannel[E any](ch <-chan E) Stream[E] {
-	return func(yield Consumer[E]) bool {
+	return func(yield Consumer[E]) {
 		for e := range ch {
 			if !yield(e) {
-				return false // Consumer saw enough.
+				break // Consumer saw enough.
 			}
 		}
-		return true
 	}
 }
 
@@ -176,18 +168,18 @@ func FromChannel[E any](ch <-chan E) Stream[E] {
 //	s := stream.FromChannelCtx(ctx, ch)
 //	out := stream.DebugString(s) // "<1, 2>"
 func FromChannelCtx[E any](ctx context.Context, ch <-chan E) Stream[E] {
-	return func(yield Consumer[E]) bool {
+	return func(yield Consumer[E]) {
 		for {
 			select {
 			case e, ok := <-ch:
 				if !ok {
-					return true
+					return // Channel closed.
 				}
 				if !yield(e) {
-					return false
+					return // Consumer saw enough.
 				}
 			case <-ctx.Done():
-				return true
+				return // Context done.
 			}
 		}
 	}

pkg/stream/generate.go

@@ -15,10 +15,10 @@ type Generator[E any] func() E
 //	s := stream.Generate(func() int { return 1	})
 //	out := stream.DebugString(s) // "<1, 1, 1, 1, 1, 1, 1, 1, 1, 1, ...>"
 func Generate[E any](next Generator[E]) Stream[E] {
-	return func(yield Consumer[E]) bool {
+	return func(yield Consumer[E]) {
 		for {
 			if !yield(next()) {
-				return false
+				return
 			}
 		}
 	}