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Puzzle 19 Explanation: Go Error

Explore the behavior of Go error interfaces in this lesson to understand why an interface may appear non-nil even if its underlying value is nil. Learn to identify common pitfalls with error handling and how to properly declare error variables to avoid such issues in Go programming.

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Try it yourself

Try executing the code below to see the result.

Go (1.16.5)
package main
import (
	"fmt"
)
type OSError int
func (e *OSError) Error() string {
	return fmt.Sprintf("error #%d", *e)
}
func FileExists(path string) (bool, error) {
	var err *OSError
	return false, err 
}
func main() {
	if _, err := FileExists("/no/such/file"); err != nil {
		fmt.Printf("error: %s\n", err)
	} else {
		fmt.Println("OK")
	}
}

Explanation

The if statement in line 19 says that err != nil, but err prints out as < nil >.

Furthermore, err in line 14 ...