struct.go: Cache structIndexes

This should help save some CPU time and avoid some memory churn.

1 files changed, 13 insertions, 1 deletions

diff --git a/struct.go b/struct.go
index b7fc287..8a664c6 100644
--- a/struct.go
+++ b/struct.go
@@ -7,6 +7,8 @@ package lowmemjson
 import (
 	"reflect"
 
+	"git.lukeshu.com/go/typedsync"
+
 	"git.lukeshu.com/go/lowmemjson/internal"
 )
 
@@ -25,9 +27,19 @@ type structIndex struct {
 	byName map[string]int
 }
 
+var structIndexCache typedsync.CacheMap[reflect.Type, structIndex]
+
 // indexStruct takes a struct Type, and indexes its fields for use by
-// Decoder.Decode() and Encoder.Encode().
+// Decoder.Decode() and Encoder.Encode().  indexStruct caches its
+// results.
 func indexStruct(typ reflect.Type) structIndex {
+	ret, _ := structIndexCache.LoadOrCompute(typ, indexStructReal)
+	return ret
+}
+
+// indexStructReal is like indexStruct, but is the real indexer,
+// bypassing the cache.
+func indexStructReal(typ reflect.Type) structIndex {
 	var byPos []structField
 	byName := make(map[string][]int)