error interface behavior

main.go

package main

import "fmt"

type MyError struct {
}

func (e MyError) Error() string {
        return "error happened"
}

func doSomething1(v bool) error {
        if !v {
                var err MyError
                return err
        }
        return nil
}

func doSomething2(v bool) error {
        var err *MyError
        if !v {
                err = &MyError{}
                return err
        }
        return err
}

func main() {
        fmt.Println("Running doSomething1(true)")
        if err := doSomething1(true); err != nil {
                fmt.Printf("\terror: %v %T\n", err, err)
        } else {
                fmt.Printf("\tno error: %v %T\n", err, err)
        }

        fmt.Println("Running doSomething1(false)")
        if err := doSomething1(false); err != nil {
                fmt.Printf("\terror: %v %T\n", err, err)
        } else {
                fmt.Printf("\tno error: %v %T\n", err, err)
        }

        fmt.Println("Running doSomething2(true)")
        if err := doSomething2(true); err != nil {
                fmt.Printf("\terror: %v %T\n", err, err)
        } else {
                fmt.Printf("\tno error: %v %T\n", err, err)
        }

        fmt.Println("Running doSomething2(false)")
        if err := doSomething2(false); err != nil {
                fmt.Printf("\terror: %v %T\n", err, err)
        } else {
                fmt.Printf("\tno error: %v %T\n", err, err)
        }
}