fix: add json serialization support for option

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

either/core.go

@@ -2,29 +2,21 @@ package either
 
 import "fmt"
 
-type EitherTag string
-
-const (
-	leftTag  = "Left"
-	rightTag = "Right"
-)
-
-// Either defines a data structure that logically holds either an E or an A. The tag discriminates the cases
-type Either[E, A any] struct {
-	tag   EitherTag `default:"Left"`
+// Either defines a data structure that logically holds either an E or an A. The flag discriminates the cases
+type (
+	Either[E, A any] struct {
+		isLeft bool
 		left   E
 		right  A
 	}
+)
 
 // String prints some debug info for the object
 func (s Either[E, A]) String() string {
-	switch s.tag {
-	case leftTag:
-		return fmt.Sprintf("%s[%T, %T](%v)", s.tag, s.left, s.right, s.left)
-	case rightTag:
-		return fmt.Sprintf("%s[%T, %T](%v)", s.tag, s.left, s.right, s.right)
+	if s.isLeft {
+		return fmt.Sprintf("Left[%T, %T](%v)", s.left, s.right, s.left)
 	}
-	return "Invalid"
+	return fmt.Sprintf("Right[%T, %T](%v)", s.left, s.right, s.right)
 }
 
 // Format prints some debug info for the object
@@ -38,19 +30,19 @@ func (s Either[E, A]) Format(f fmt.State, c rune) {
 }
 
 func IsLeft[E, A any](val Either[E, A]) bool {
-	return val.tag == leftTag
+	return val.isLeft
 }
 
 func IsRight[E, A any](val Either[E, A]) bool {
-	return val.tag == rightTag
+	return !val.isLeft
 }
 
 func Left[E, A any](value E) Either[E, A] {
-	return Either[E, A]{tag: leftTag, left: value}
+	return Either[E, A]{isLeft: true, left: value}
 }
 
 func Right[E, A any](value A) Either[E, A] {
-	return Either[E, A]{tag: rightTag, right: value}
+	return Either[E, A]{isLeft: false, right: value}
 }
 
 func MonadFold[E, A, B any](ma Either[E, A], onLeft func(e E) B, onRight func(a A) B) B {

either/either_test.go

@@ -11,6 +11,12 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
+func TestDefault(t *testing.T) {
+	var e Either[error, string]
+
+	assert.Equal(t, Of[error](""), e)
+}
+
 func TestIsLeft(t *testing.T) {
 	err := errors.New("Some error")
 	withError := Left[error, string](err)

option/core.go

@@ -6,32 +6,22 @@ import (
 	"fmt"
 )
 
-type OptionTag string
-
-const (
-	noneTag = "None"
-	someTag = "Some"
-)
-
 var (
 	jsonNull = []byte("null")
 )
 
 // Option defines a data structure that logically holds a value or not
 type Option[A any] struct {
-	tag   OptionTag `default:"None"`
-	value A
+	isSome bool
+	some   A
 }
 
 // String prints some debug info for the object
 func (s Option[A]) String() string {
-	switch s.tag {
-	case noneTag:
-		return fmt.Sprintf("%s[%T]", s.tag, s.value)
-	case someTag:
-		return fmt.Sprintf("%s[%T](%v)", s.tag, s.value, s.value)
+	if s.isSome {
+		return fmt.Sprintf("Some[%T](%v)", s.some, s.some)
 	}
-	return "Invalid"
+	return fmt.Sprintf("None[%T]", s.some)
 }
 
 // Format prints some debug info for the object
@@ -45,28 +35,29 @@ func (s Option[A]) Format(f fmt.State, c rune) {
 }
 
 func (s Option[A]) MarshalJSON() ([]byte, error) {
-	if s.tag == noneTag {
+	if IsSome(s) {
+		return json.Marshal(s.some)
+	}
 	return jsonNull, nil
 }
-	return json.Marshal(s.value)
-}
 
-func (s Option[A]) UnmarshalJSON(data []byte) error {
+func (s *Option[A]) UnmarshalJSON(data []byte) error {
 	// decode the value
 	if bytes.Equal(data, jsonNull) {
-		s.tag = noneTag
+		s.isSome = false
+		s.some = *new(A)
 		return nil
 	}
-	s.tag = someTag
-	return json.Unmarshal(data, &s.value)
+	s.isSome = true
+	return json.Unmarshal(data, &s.some)
 }
 
 func IsNone[T any](val Option[T]) bool {
-	return val.tag == noneTag
+	return !val.isSome
 }
 
 func Some[T any](value T) Option[T] {
-	return Option[T]{tag: someTag, value: value}
+	return Option[T]{isSome: true, some: value}
 }
 
 func Of[T any](value T) Option[T] {
@@ -74,20 +65,20 @@ func Of[T any](value T) Option[T] {
 }
 
 func None[T any]() Option[T] {
-	return Option[T]{tag: noneTag}
+	return Option[T]{isSome: false}
 }
 
 func IsSome[T any](val Option[T]) bool {
-	return val.tag == someTag
+	return val.isSome
 }
 
 func MonadFold[A, B any](ma Option[A], onNone func() B, onSome func(A) B) B {
-	if IsNone(ma) {
-		return onNone()
+	if IsSome(ma) {
+		return onSome(ma.some)
 	}
-	return onSome(ma.value)
+	return onNone()
 }
 
 func Unwrap[A any](ma Option[A]) (A, bool) {
-	return ma.value, ma.tag == someTag
+	return ma.some, ma.isSome
 }

option/option_test.go

@@ -1,14 +1,59 @@
 package option
 
 import (
+	"encoding/json"
 	"fmt"
 	"testing"
 
 	F "github.com/ibm/fp-go/function"
 	"github.com/ibm/fp-go/internal/utils"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
+type (
+	SampleData struct {
+		Value    string
+		OptValue Option[string]
+	}
+)
+
+func TestJson(t *testing.T) {
+
+	sample := SampleData{
+		Value:    "value",
+		OptValue: Of("optValue"),
+	}
+
+	data, err := json.Marshal(&sample)
+	require.NoError(t, err)
+
+	var deser SampleData
+	err = json.Unmarshal(data, &deser)
+	require.NoError(t, err)
+
+	assert.Equal(t, sample, deser)
+
+	sample = SampleData{
+		Value:    "value",
+		OptValue: None[string](),
+	}
+
+	data, err = json.Marshal(&sample)
+	require.NoError(t, err)
+
+	err = json.Unmarshal(data, &deser)
+	require.NoError(t, err)
+
+	assert.Equal(t, sample, deser)
+}
+
+func TestDefault(t *testing.T) {
+	var e Option[string]
+
+	assert.Equal(t, None[string](), e)
+}
+
 func TestReduce(t *testing.T) {
 
 	assert.Equal(t, 2, F.Pipe1(None[int](), Reduce(utils.Sum, 2)))