website/sl/sl.go

package sl

import (
	"fmt"
	"log"
)

type SlotKey[T any] *struct{}

func NewSlot[T any]() SlotKey[T] {
	return SlotKey[T](new(struct{}))
}

type slot struct {
	createFunc func(*ServiceLocator) (any, error)
	created    bool
	value      any

	typ string
}

func (s *slot) checkInitialized(l *ServiceLocator) error {
	if !s.created {
		v, err := s.createFunc(l)
		if err != nil {
			return err
		}

		log.Printf(`initialized lazy value of type %T for slot of type %s`, v, s.typ)

		s.created = true
		s.value = v
	}

	return nil
}

type ServiceLocator struct {
	providers map[any]*slot
}

func New() *ServiceLocator {
	return &ServiceLocator{
		providers: map[any]*slot{},
	}
}

func InjectValue[T any](l *ServiceLocator, slotKey SlotKey[T], value T) T {
	log.Printf(`injected value of type %T for slot of type %s`, value, getTypeName[T]())

	l.providers[slotKey] = &slot{
		nil,
		true,
		value,
		getTypeName[T](),
	}
	return value
}

func InjectLazy[T any](l *ServiceLocator, slotKey SlotKey[T], createFunc func(*ServiceLocator) (T, error)) {
	log.Printf(`injected lazy for slot of type %s`, getTypeName[T]())

	l.providers[slotKey] = &slot{
		createFunc: func(l *ServiceLocator) (any, error) {
			return createFunc(l)
		},
		created: false,
		value:   nil,
		typ:     getTypeName[T](),
	}
}

func Use[T any](l *ServiceLocator, slotKey SlotKey[T]) (T, error) {
	var zero T

	slot, ok := l.providers[slotKey]
	if !ok {
		return zero, fmt.Errorf(`no injected value for type %s`, getTypeName[T]())
	}

	err := slot.checkInitialized(l)
	if err != nil {
		return zero, err
	}

	v := slot.value.(T)

	log.Printf(`using slot of type %s with value of type %T`, getTypeName[T](), v)
	return v, nil
}

// // Require forces the initialization of a slot
// func Require[T any](l *ServiceLocator, slotKey SlotKey[T]) error {
// 	var zero T

// 	slot, ok := l.providers[slotKey]
// 	if !ok {
// 		return fmt.Errorf(`no injected value for type %T`, zero)
// 	}

// 	return slot.checkInitialized(l)
// }

// // MustRequire forces the initialization of a slot or panics if the slot is missing
// func MustRequire[T any](l *ServiceLocator, slotKey SlotKey[T]) {
// 	err := Require(l, slotKey)
// 	if err != nil {
// 		panic(err)
// 	}
// }

// // Inject will set the implementation for "S" to "value" (the service will be initialized when needed after all of its dependencies)
// func Inject[S Service](l *Context, value S) {
// 	key := getTypeName[S]()
// 	log.Printf(`injecting value of type %T for interface %s`, value, key)

// 	l.providers[key] = &provider{false, nil, value}
// }

// // InjectValue will set the implementation for "S" to "value" and mark this service as already initialized (as this is just a constant)
// func InjectValue[S Service](l *Context, value S) S {
// 	key := getTypeName[S]()
// 	log.Printf(`injecting value of type %T for interface %s`, value, key)

// 	l.providers[key] = &provider{true, nil, value}
// 	return value
// }

// // Use will retrive from the service locator the implementation set for the type "T" and initialize the service if yet to be initialized
// func Use[T Service](l *Context) (T, error) {
// 	provider, ok := l.providers[getTypeName[T]()]
// 	if !ok {
// 		var zero T
// 		return zero, fmt.Errorf(`no injected value for type "%T"`, zero)
// 	}

// 	if provider.initialized {
// 		service := provider.service.(T)
// 		return service, nil
// 	}

// 	log.Printf(`initializing %T`, provider.service)
// 	if err := provider.service.Initialize(l); err != nil {
// 		var zero T
// 		return zero, err
// 	}

// 	provider.initialized = true
// 	service := provider.service.(T)
// 	return service, nil
// }

func getTypeName[T any]() string {
	var zero T
	return fmt.Sprintf(`%T`, &zero)[1:]
}