func (f Float64) Present() bool {
	return f.value != nil
}
Present returns whether or not the value is present.
package optional
import (
	"encoding/json"
	"errors"
)
type Float64 struct {
	value *float64
}
func NewFloat64(v float64) Float64 {
	return Float64{&v}
}
func (f *Float64) Set(v float64) {
	f.value = &v
}
func (f Float64) Get() (float64, error) {
	if !f.Present() {
		var zero float64
		return zero, errors.New("value not present")
	}
	return *f.value, nil
}
func (f Float64) MustGet() float64 {
	if !f.Present() {
		panic("value not present")
	}
	return *f.value
}