Minimal shared cache for struct field paths

targets.go

@@ -5,6 +5,7 @@ import (
 	"math"
 	"reflect"
 	"strings"
+	"sync"
 )
 
 type target interface {
@@ -466,10 +467,37 @@ func scopeMap(v reflect.Value, name string) (target, bool, error) {
 	}, true, nil
 }
 
+type fieldPathsMap = map[string][]int
+
+type fieldPathsCache struct {
+	m map[reflect.Type]fieldPathsMap
+	l sync.RWMutex
+}
+
+func (c *fieldPathsCache) get(t reflect.Type) (fieldPathsMap, bool) {
+	c.l.RLock()
+	paths, ok := c.m[t]
+	c.l.RUnlock()
+	return paths, ok
+}
+
+func (c *fieldPathsCache) set(t reflect.Type, m fieldPathsMap) {
+	c.l.Lock()
+	c.m[t] = m
+	c.l.Unlock()
+}
+
+var globalFieldPathsCache = fieldPathsCache{
+	m: map[reflect.Type]fieldPathsMap{},
+	l: sync.RWMutex{},
+}
+
 func scopeStruct(v reflect.Value, name string) (target, bool, error) {
 	// TODO: cache this, and reduce allocations
 
-	fieldPaths := map[string][]int{}
+	fieldPaths, ok := globalFieldPathsCache.get(v.Type())
+	if !ok {
+		fieldPaths = map[string][]int{}
 
 		path := make([]int, 0, 16)
 		var walk func(reflect.Value)
@@ -502,6 +530,9 @@ func scopeStruct(v reflect.Value, name string) (target, bool, error) {
 
 		walk(v)
 
+		globalFieldPathsCache.set(v.Type(), fieldPaths)
+	}
+
 	path, ok := fieldPaths[name]
 	if !ok {
 		path, ok = fieldPaths[strings.ToLower(name)]