json: create codecCache type

Author: extemporalgenome

json/codec.go

@@ -72,13 +72,15 @@ type (
 	sortFunc  func([]reflect.Value)
 )
 
+type codecCache map[unsafe.Pointer]codec
+
 // Eventually consistent cache mapping go types to dynamically generated
 // codecs.
 //
 // Note: using a uintptr as key instead of reflect.Type shaved ~15ns off of
 // the ~30ns Marhsal/Unmarshal functions which were dominated by the map
 // lookup time for simple types like bool, int, etc..
-var cache atomic.Pointer[map[unsafe.Pointer]codec]
+var cache atomic.Pointer[codecCache]
 
 func cachedCodec(t reflect.Type) codec {
 	cache := cacheLoad()
@@ -91,7 +93,7 @@ func cachedCodec(t reflect.Type) codec {
 	return c
 }
 
-func cacheLoad() map[unsafe.Pointer]codec {
+func cacheLoad() codecCache {
 	p := cache.Load()
 	if p == nil {
 		return nil
@@ -100,8 +102,8 @@ func cacheLoad() map[unsafe.Pointer]codec {
 	return *p
 }
 
-func cacheStore(typ reflect.Type, cod codec, oldCodecs map[unsafe.Pointer]codec) {
-	newCodecs := make(map[unsafe.Pointer]codec, len(oldCodecs)+1)
+func cacheStore(typ reflect.Type, cod codec, oldCodecs codecCache) {
+	newCodecs := make(codecCache, len(oldCodecs)+1)
 	maps.Copy(newCodecs, oldCodecs)
 	newCodecs[typeid(typ)] = cod