read.go
func (v Value) Float64() float64 {
	x, ok := v.data.(float64)
	if !ok {
		x, ok := v.data.(int64)
		if ok {
			return float64(x)
		}
		return 0
	}
	return x
}
func (v Value) Float64() float64 {
	x, ok := v.data.(float64)
	if !ok {
		x, ok := v.data.(int64)
		if ok {
			return float64(x)
		}
		return 0
	}
	return x
}
// Float64 returns v's float64 value, converting from integer if necessary.
// If v.Kind() != Float64 and v.Kind() != Int64, Float64 returns 0.