types/nil.go

package types

import (
	"fmt"
	"encoding/json"
)

// The type represents the type safe nullable values
// without pointers.
type Nilable[V any] struct {
	value V
	valid bool
}

var _ = MustImplement[interface{
	fmt.Stringer
	json.Marshaler
}](
	Nilable[Empty]{},
)

var _ = MustImplement[interface{
	json.Unmarshaler
}](
	&Nilable[Empty]{},
)

func (n Nilable[V]) String() string {
	if !n.IsValid() {
		return "<nil>"
	
	}
	return fmt.Sprintf("%v", n.value)
}

func (n Nilable[V]) MarshalJSON() ([]byte, error) {
	if !n.valid {
		return []byte("null"), nil
	}

	return json.Marshal(n.value)
}

func (n *Nilable[V]) UnmarshalJSON(data []byte) error {
	if string(data) == "null" {
		var v [1]V
		n.valid = false
		n.value = v[0]
		return nil
	}

	err := json.Unmarshal(data, &n.value)
	if err != nil {
		return err
	}

	n.valid = true

	return nil
}

// Returns the the null of specified type.
func Nil[V any]() Nilable[V] {
	return Nilable[V]{}
}

func Valid[V any](v V) Nilable[V] {
	return Nilable[V]{
		valid: true,
		value: v,
	}
}

// Returns the value and the validity of the value.
func (n Nilable[V]) Got() (V, bool) {
	var buf [1]V
	if !n.valid {
		return buf[0], false
	}

	return n.value, n.valid
}

// Returns true if is not null.
func (n Nilable[V]) IsValid() bool {
	return n.valid
}