errors.go

type MyLongTypeName struct{
	...
}

func foo(x int, y string) (MyLongTypeName, error) {
	if x == 42 {
		return MyLongTypeName{}, errors.New("x cannot be the meaning of life")
	}

	if y == "" {
		return MyLongTypeName{}, errors.New("y cannot be empty")
	}

	return MyLongTypeName{...}, nil
}