driver

type Variable struct {
	Value      interface{}
	UpdateTime time.Time
}

type Watcher interface {
	// WatchVariable blocks until the variable changes, the Context's Done channel closes or an
	// error occurs.
	//
	// If the variable has changed, then method should return a Variable object with the
	// new value.
	//
	// It is recommended that an implementation should avoid returning the same error of the
	// previous WatchVariable call if the implementation can detect such and treat as no changes had
	// incurred instead.  A sample case is when the variable is deleted, WatchVariable should return an
	// error upon initial detection.  A succeeding WatchVariable call may decide to block until
	// the variable source is restored.
	//
	// To stop this function from blocking, caller can passed in Context object constructed via
	// WithCancel and call the cancel function.
	WatchVariable(context.Context) (Variable, error)
	// Close cleans up any resources used by the Watcher object.
	Close() error
}