refactor: make error handling simpler and more go-like

todo/list.go

@@ -1,14 +1,14 @@
 package todo
 
-type UserError struct {
- message string
-}
-
-var ErrorBadId = &UserError{"bad todoItemId"}
-
-func (ue *UserError) Error() string {
- return ue.message
-}
+import (
+ "errors"
+ "fmt"
+)
+
+var (
+ UserError = errors.New("user error")
+ ErrorBadId = fmt.Errorf("%w: bad todoItemId", UserError)
+)
 
 type Item struct {
  Title string

web/handlers.go

@@ -1,6 +1,7 @@
 package web
 
 import (
+ "errors"
  "github.com/xpmatteo/todomvc-golang/todo"
  "html/template"
  "log"
@@ -87,12 +88,10 @@ func ToggleHandler(templ *template.Template, repository Repository) http.Handler
  })
 }
 
-//goland:noinspection GoTypeAssertionOnErrors
 func handleError(w http.ResponseWriter, err error) {
- switch err.(type) {
- case *todo.UserError:
+ if errors.Is(err, todo.UserError) {
  badRequest(w, err)
- default:
+ } else {
  internalServerError(w, err)
  }
 }

web/handlers_test.go

@@ -106,7 +106,7 @@ func Test_editHandler_elementNotFound(t *testing.T) {
  EditHandler(templ, repository).ServeHTTP(w, r)
 
  assert.Equal(http.StatusBadRequest, w.Code)
- assert.Equal("bad todoItemId\n", w.Body.String())
+ assert.Equal("user error: bad todoItemId\n", w.Body.String())
 }
 
 func Test_toggleHandler_ok(t *testing.T) {