fix: Add custom marshal/unmarshal to immutable.Option

Add custom marshal/unmarshal to immutable.Option

option.go

@@ -1,5 +1,7 @@
 package immutable
 
+import "encoding/json"
+
 // Option represents an item that may or may not have a value.
 type Option[T any] struct {
 	// If HasValue is true, this Option contains a value, if
@@ -23,7 +25,7 @@ func None[T any]() Option[T] {
 	return Option[T]{}
 }
 
-// HasValue returns a boolean indicating whether or not this optino contains a value. If
+// HasValue returns a boolean indicating whether or not this option contains a value. If
 // it returns true, this Option contains a value, if it is false it contains no value.
 func (o Option[T]) HasValue() bool {
 	return o.hasValue
@@ -34,3 +36,26 @@ func (o Option[T]) HasValue() bool {
 func (o Option[T]) Value() T {
 	return o.value
 }
+
+// MarshalJSON implements the json.Marshaler interface.
+func (o Option[T]) MarshalJSON() ([]byte, error) {
+	if o.HasValue() {
+		return json.Marshal(o.Value())
+	}
+	return []byte("null"), nil
+}
+
+// UnmarshalJSON implements the json.Unmarshaler interface.
+func (o *Option[T]) UnmarshalJSON(b []byte) error {
+	if string(b) == "null" {
+		*o = None[T]()
+		return nil
+	}
+	var value T
+	err := json.Unmarshal(b, &value)
+	if err != nil {
+		return err
+	}
+	*o = Some(value)
+	return nil
+}

option_test.go

@@ -0,0 +1,70 @@
+package immutable
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+func TestSome(t *testing.T) {
+	opt := Some(1)
+	if !opt.HasValue() {
+		t.Errorf("expected Some to return an Option with a value")
+	}
+	if opt.Value() != 1 {
+		t.Errorf("expected Some to return an Option with a value of 1")
+	}
+}
+
+func TestNone(t *testing.T) {
+	opt := None[int]()
+	if opt.HasValue() {
+		t.Errorf("expected None to return an Option with no value")
+	}
+}
+
+func TestOptionMarshal(t *testing.T) {
+	opt := Some(1)
+	b, err := json.Marshal(opt)
+	if err != nil {
+		t.Errorf("expected no error, got %v", err)
+	}
+	if string(b) != "1" {
+		t.Errorf("expected 1, got %s", b)
+	}
+}
+
+func TestOptionMarshalNone(t *testing.T) {
+	opt := None[int]()
+	b, err := json.Marshal(opt)
+	if err != nil {
+		t.Errorf("expected no error, got %v", err)
+	}
+	if string(b) != "null" {
+		t.Errorf("expected null, got %s", b)
+	}
+}
+
+func TestOptionUnmarshal(t *testing.T) {
+	var opt Option[int]
+	err := json.Unmarshal([]byte("1"), &opt)
+	if err != nil {
+		t.Errorf("expected no error, got %v", err)
+	}
+	if !opt.HasValue() {
+		t.Errorf("expected Some to return an Option with a value")
+	}
+	if opt.Value() != 1 {
+		t.Errorf("expected Some to return an Option with a value of 1")
+	}
+}
+
+func TestOptionUnmarshalNone(t *testing.T) {
+	var opt Option[int]
+	err := json.Unmarshal([]byte("null"), &opt)
+	if err != nil {
+		t.Errorf("expected no error, got %v", err)
+	}
+	if opt.HasValue() {
+		t.Errorf("expected None to return an Option with no value")
+	}
+}