Add Result type (#16)

* 👷 adding test and push coverage

* ⬆️ use official Go 1.18 image

* ✨ result interface

* delete commented code

Co-authored-by: Ruidy <rnemausat@newstore.com>

result.go

@@ -0,0 +1,49 @@
+package underscore
+
+// Result represent the outcome of an operation where failure is possible
+type Result[T any] interface {
+	isResult() //to seal the Result interface
+	ToValue() (*T, error)
+	IsSuccess() bool
+}
+
+// Ok is the Result that represents success.
+type Ok[T any] struct {
+	Value *T
+}
+
+func (Ok[T]) isResult() {}
+
+func (o Ok[T]) ToValue() (*T, error) {
+	return o.Value, nil
+}
+
+func (o Ok[T]) IsSuccess() bool {
+	return true
+}
+
+// Err is the Result that represents failure. It implements the error interface
+type Err[T any] struct{ Err error }
+
+func (e Err[T]) ToValue() (*T, error) {
+	return nil, e.Err
+}
+
+func (e Err[T]) IsSuccess() bool {
+	return false
+}
+
+func (Err[T]) isResult() {}
+
+func (e Err[T]) Error() string {
+	return e.Err.Error()
+}
+
+func ToResult[T any](value *T, err error) Result[T] {
+	if err != nil {
+		return Err[T]{
+			Err: err,
+		}
+	}
+	return Ok[T]{Value: value}
+}

result_test.go

@@ -0,0 +1,41 @@
+package underscore_test
+
+import (
+	"errors"
+	"testing"
+
+	u "github.com/rjNemo/underscore"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestSuccess(t *testing.T) {
+	res := isAnswerToLife(42)
+	assert.True(t, res.IsSuccess())
+}
+
+func TestFailure(t *testing.T) {
+	res := isAnswerToLife(13)
+	assert.False(t, res.IsSuccess())
+}
+
+func TestIsOK(t *testing.T) {
+	res, err := isAnswerToLife(42).ToValue()
+	assert.NoError(t, err)
+	assert.Equal(t, "You get it", *res)
+}
+
+func TestIsError(t *testing.T) {
+	life := isAnswerToLife(13)
+	res, err := life.ToValue()
+	assert.Error(t, err)
+	assert.Equal(t, "nope", life.(u.Err[string]).Error())
+	assert.Nil(t, res)
+}
+
+func isAnswerToLife(num int) u.Result[string] {
+	if num == 42 {
+		res := "You get it"
+		return u.ToResult(&res, nil)
+	}
+	return u.ToResult[string](nil, errors.New("nope"))
+}