Code:play 

package main

import (
	"fmt"
	"time"
)

// MyError is an error implementation that includes a time and message.
type MyError struct {
	When time.Time
	What string
}

func (e MyError) Error() string {
	return fmt.Sprintf("%v: %v", e.When, e.What)
}

func oops() error {
	return MyError{
		time.Date(1989, 3, 15, 22, 30, 0, 0, time.UTC),
		"the file system has gone away",
	}
}

func main() {
	if err := oops(); err != nil {
		fmt.Println(err)
	}
}

Output:

1989-03-15 22:30:00 +0000 UTC: the file system has gone away

Code:play 

package main

import (
	"errors"
	"fmt"
)

func main() {
	err := errors.New("emit macho dwarf: elf header corrupted")
	if err != nil {
		fmt.Print(err)
	}
}

Output:

emit macho dwarf: elf header corrupted

The fmt package's Errorf function lets us use the package's formatting features to create descriptive error messages.

Code:play 

package main

import (
	"fmt"
)

func main() {
	const name, id = "bimmler", 17
	err := fmt.Errorf("user %q (id %d) not found", name, id)
	if err != nil {
		fmt.Print(err)
	}
}

Output:

user "bimmler" (id 17) not found