--- /dev/null
+package main
+
+import (
+ "fmt"
+ "os"
+)
+
+type CustomError struct {
+ Err string
+}
+
+func (ce CustomError) Error() string {
+ return ce.Err
+}
+
+func SomeFunc() (string, *CustomError) {
+ return "hello", nil
+}
+
+func main() {
+ // Do something that creates a variable err of type error
+ _, err := os.Open("/")
+ if err != nil {
+ panic(err)
+ }
+
+ // Then replace the err type with *CustomError
+ val, err := SomeFunc()
+ if err != nil { // want `this comparison is always true`
+ panic(err)
+ }
+
+ fmt.Println("No problem", val)
+}