1package sentinel
 2
 3import (
 4	"github.com/openai/openai-go/internal/encoding/json/shims"
 5	"reflect"
 6	"sync"
 7)
 8
 9type cacheEntry struct {
10	x    any
11	ptr  uintptr
12	kind reflect.Kind
13}
14
15var nullCache sync.Map // map[reflect.Type]cacheEntry
16
17func NewNullSentinel[T any](mk func() T) T {
18	t := shims.TypeFor[T]()
19	entry, loaded := nullCache.Load(t) // avoid premature allocation
20	if !loaded {
21		x := mk()
22		ptr := reflect.ValueOf(x).Pointer()
23		entry, _ = nullCache.LoadOrStore(t, cacheEntry{x, ptr, t.Kind()})
24	}
25	return entry.(cacheEntry).x.(T)
26}
27
28// for internal use only
29func IsValueNull(v reflect.Value) bool {
30	switch v.Kind() {
31	case reflect.Map, reflect.Slice:
32		null, ok := nullCache.Load(v.Type())
33		return ok && v.Pointer() == null.(cacheEntry).ptr
34	}
35	return false
36}
37
38func IsNull[T any](v T) bool {
39	t := shims.TypeFor[T]()
40	switch t.Kind() {
41	case reflect.Map, reflect.Slice:
42		null, ok := nullCache.Load(t)
43		return ok && reflect.ValueOf(v).Pointer() == null.(cacheEntry).ptr
44	}
45	return false
46}