checker.go

type Checker struct {
	err error
}

func (c *Checker) Check(cond bool, err error) {
	if !cond && c.err == nil {
		c.err = err
	}
}

func (c *Checker) Checkf(cond bool, format string, args ...string) {
	c.Check(cond, fmt.Errorf(format, args...))
}

func (c Checker) Err() error {
	return c.err
}