fix: bug in compact array (#87)

Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com>

either/array.go

@@ -61,14 +61,14 @@ func SequenceArray[E, A any](ma []Either[E, A]) Either[E, []A] {
 	return SequenceArrayG[[]A](ma)
 }
 
-// CompactArrayG discards the none values and keeps the some values
+// CompactArrayG discards the none values and keeps the right values
 func CompactArrayG[A1 ~[]Either[E, A], A2 ~[]A, E, A any](fa A1) A2 {
 	return RA.Reduce(fa, func(out A2, value Either[E, A]) A2 {
 		return MonadFold(value, F.Constant1[E](out), F.Bind1st(RA.Append[A2, A], out))
-	}, make(A2, len(fa)))
+	}, make(A2, 0, len(fa)))
 }
 
-// CompactArray discards the none values and keeps the some values
+// CompactArray discards the none values and keeps the right values
 func CompactArray[E, A any](fa []Either[E, A]) []A {
 	return CompactArrayG[[]Either[E, A], []A](fa)
 }

either/array_test.go

@@ -0,0 +1,18 @@
+package either
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestCompactArray(t *testing.T) {
+	ar := []Either[string, string]{
+		Of[string]("ok"),
+		Left[string]("err"),
+		Of[string]("ok"),
+	}
+
+	res := CompactArray(ar)
+	assert.Equal(t, 2, len(res))
+}

option/array.go

@@ -65,7 +65,7 @@ func SequenceArray[A any](ma []Option[A]) Option[[]A] {
 func CompactArrayG[A1 ~[]Option[A], A2 ~[]A, A any](fa A1) A2 {
 	return RA.Reduce(fa, func(out A2, value Option[A]) A2 {
 		return MonadFold(value, F.Constant(out), F.Bind1st(RA.Append[A2, A], out))
-	}, make(A2, len(fa)))
+	}, make(A2, 0, len(fa)))
 }
 
 // CompactArray discards the none values and keeps the some values

option/array_test.go

@@ -34,3 +34,14 @@ func TestSequenceArray(t *testing.T) {
 
 	assert.Equal(t, res, Of([]int{1, 2}))
 }
+
+func TestCompactArray(t *testing.T) {
+	ar := []Option[string]{
+		Of("ok"),
+		None[string](),
+		Of("ok"),
+	}
+
+	res := CompactArray(ar)
+	assert.Equal(t, 2, len(res))
+}