list: fix Append & Prepend, remove varargs support

Similar reason for the API change as the previous commit.

2 files changed, 17 insertions, 12 deletions

diff --git a/immutable.go b/immutable.go
index e43bc70..666bb49 100644
--- a/immutable.go
+++ b/immutable.go
@@ -117,12 +117,8 @@ func (l *List[T]) set(index int, value T, mutable bool) *List[T] {
 }
 
 // Append returns a new list with value added to the end of the list.
-func (l *List[T]) Append(values ...T) *List[T] {
-	other := l.clone()
-	for _, value := range values {
-		other.append(value, true)
-	}
-	return other
+func (l *List[T]) Append(value T) *List[T] {
+	return l.append(value, false)
 }
 
 func (l *List[T]) append(value T, mutable bool) *List[T] {
@@ -145,12 +141,8 @@ func (l *List[T]) append(value T, mutable bool) *List[T] {
 }
 
 // Prepend returns a new list with value(s) added to the beginning of the list.
-func (l *List[T]) Prepend(values ...T) *List[T] {
-	other := l.clone()
-	for i := len(values) - 1; i >= 0; i-- {
-		other.prepend(values[i], true)
-	}
-	return other
+func (l *List[T]) Prepend(value T) *List[T] {
+	return l.prepend(value, false)
 }
 
 func (l *List[T]) prepend(value T, mutable bool) *List[T] {
diff --git a/immutable_test.go b/immutable_test.go
index a878a78..9a0de37 100644
--- a/immutable_test.go
+++ b/immutable_test.go
@@ -223,6 +223,19 @@ func TestList(t *testing.T) {
 		}
 	})
 
+	t.Run("AppendImmutable", func(t *testing.T) {
+		outer_l := NewList[int]()
+		for N := 0; N < 1_000; N++ {
+			l1 := outer_l.Append(0)
+			outer_l.Append(1)
+			if actual := l1.Get(N); actual != 0 {
+				t.Fatalf("Append mutates list with %d elements. Got %d instead of 0", N, actual)
+			}
+
+			outer_l = outer_l.Append(0)
+		}
+	})
+
 	RunRandom(t, "Random", func(t *testing.T, rand *rand.Rand) {
 		l := NewTList()
 		for i := 0; i < 100000; i++ {