fix: refactor either type (#102)

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

either/core.go

@@ -23,17 +23,16 @@ type (
 	// Either defines a data structure that logically holds either an E or an A. The flag discriminates the cases
 	Either[E, A any] struct {
 		isLeft bool
-		left   E
-		right  A
+		value  any
 	}
 )
 
 // String prints some debug info for the object
 func (s Either[E, A]) String() string {
 	if s.isLeft {
-		return fmt.Sprintf("Left[%T, %T](%v)", s.left, s.right, s.left)
+		return fmt.Sprintf("Left[%T](%v)", s.value, s.value)
 	}
-	return fmt.Sprintf("Right[%T, %T](%v)", s.left, s.right, s.right)
+	return fmt.Sprintf("Right[%T](%v)", s.value, s.value)
 }
 
 // Format prints some debug info for the object
@@ -58,23 +57,29 @@ func IsRight[E, A any](val Either[E, A]) bool {
 
 // Left creates a new instance of an [Either] representing the left value.
 func Left[A, E any](value E) Either[E, A] {
-	return Either[E, A]{isLeft: true, left: value}
+	return Either[E, A]{true, value}
 }
 
 // Right creates a new instance of an [Either] representing the right value.
 func Right[E, A any](value A) Either[E, A] {
-	return Either[E, A]{isLeft: false, right: value}
+	return Either[E, A]{false, value}
 }
 
 // MonadFold extracts the values from an [Either] by invoking the [onLeft] callback or the [onRight] callback depending on the case
 func MonadFold[E, A, B any](ma Either[E, A], onLeft func(e E) B, onRight func(a A) B) B {
 	if ma.isLeft {
-		return onLeft(ma.left)
+		return onLeft(ma.value.(E))
 	}
-	return onRight(ma.right)
+	return onRight(ma.value.(A))
 }
 
 // Unwrap converts an [Either] into the idiomatic tuple
 func Unwrap[E, A any](ma Either[E, A]) (A, E) {
-	return ma.right, ma.left
+	if ma.isLeft {
+		var a A
+		return a, ma.value.(E)
+	} else {
+		var e E
+		return ma.value.(A), e
+	}
 }

either/either_test.go

@@ -26,12 +26,6 @@ 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[string](err)

either/examples_create_test.go

@@ -48,11 +48,11 @@ func ExampleEither_creation() {
 	fmt.Println(rightFromPred)
 
 	// Output:
-	// Left[*errors.errorString, string](some error)
-	// Right[<nil>, string](value)
-	// Left[*errors.errorString, *string](value was nil)
+	// Left[*errors.errorString](some error)
+	// Right[string](value)
+	// Left[*errors.errorString](value was nil)
 	// true
-	// Left[*errors.errorString, int](3 is an odd number)
-	// Right[<nil>, int](4)
+	// Left[*errors.errorString](3 is an odd number)
+	// Right[int](4)
 
 }

either/examples_extract_test.go

@@ -53,8 +53,8 @@ func ExampleEither_extraction() {
 	fmt.Println(doubleFromRightBis)
 
 	// Output:
-	// Left[*errors.errorString, int](Division by Zero!)
-	// Right[<nil>, int](10)
+	// Left[*errors.errorString](Division by Zero!)
+	// Right[int](10)
 	// 0
 	// 10
 	// 0