read.go
func (v Value) Int64() int64 {
	x, ok := v.data.(int64)
	if !ok {
		return 0
	}
	return x
}
func (v Value) Int64() int64 {
	x, ok := v.data.(int64)
	if !ok {
		return 0
	}
	return x
}
// Int64 returns v's int64 value.
// If v.Kind() != Int64, Int64 returns 0.