From b6efa35b03639989586fcd7a0c1a765fb402562f Mon Sep 17 00:00:00 2001
From: Carsten Leue <CarstenLeue@users.noreply.github.com>
Date: Wed, 29 Nov 2023 22:13:46 +0100
Subject: [PATCH] fix: bug in compact array (#87)

Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com>
---
 either/array.go      |  6 +++---
 either/array_test.go | 18 ++++++++++++++++++
 option/array.go      |  2 +-
 option/array_test.go | 11 +++++++++++
 4 files changed, 33 insertions(+), 4 deletions(-)
 create mode 100644 either/array_test.go

diff --git a/either/array.go b/either/array.go
index f3151dd..c7326aa 100644
--- a/either/array.go
+++ b/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)
 }
diff --git a/either/array_test.go b/either/array_test.go
new file mode 100644
index 0000000..523c1b9
--- /dev/null
+++ b/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))
+}
diff --git a/option/array.go b/option/array.go
index 2fd02b1..25050ee 100644
--- a/option/array.go
+++ b/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
diff --git a/option/array_test.go b/option/array_test.go
index a4c67bb..2a31baa 100644
--- a/option/array_test.go
+++ b/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))
+}