i have a silly idea

ent/class.go

@@ -14,11 +14,15 @@ type Class struct {
 	// all other entities for this class use this instance as a prototype
 	baseline *Entity
 
+	// maps field names back to their indexes. Entities use this to access
+	// their own fields by name instead of by slot.
+	fieldNames map[string]int
+
 	fp *fieldPath
 }
 
 func (c *Class) New() *Entity {
-	return &Entity{Class: c, fields: make(map[string]interface{}, len(c.Fields))}
+	return &Entity{Class: c}
 }
 
 func (c Class) String() string {

ent/entity.go

@@ -8,7 +8,6 @@ import (
 
 type Entity struct {
 	*Class
-	fields map[string]interface{}
 }
 
 func (e *Entity) Read(br bit.Reader) error {

ent/fieldpath.go

@@ -7,16 +7,26 @@ import (
 
 type fieldPath struct {
 	// slice of values, to be reused over and over
-	vals []int
+	vals [6]int
+
 	// index of the last valid value. e.g., the head of the stack.
 	last int
 
-	history [][]int
+	// history of fieldpath values. that is, all selections thus far.
+	// Everything is fixed width to avoid allocations as much as possible
+	// inside of the fieldpath stuff. history lengths are known to go over 500,
+	// but I honestly have no idea if there is or isn't a limit. this is a
+	// hazard.
+	history [1024][7]int
+
+	// last valid index of a history entry
+	hlast int
 }
 
 func newFieldPath() *fieldPath {
-	f := &fieldPath{vals: make([]int, 32)}
+	f := new(fieldPath)
 	f.vals[f.last] = -1
+	f.hlast = -1
 	return f
 }
 
@@ -50,11 +60,29 @@ func (f *fieldPath) read(br bit.Reader, n node, class *Class) error {
 		}
 		fn(f, br)
 		Debug.Printf("fieldpath: %v", f.path())
-		// Debug.Printf("fieldpath: %v", f.getField(class))
+		f.keep()
 	}
 	return nil
 }
 
+// adds our current vals to the history list.
+// a history list entry is an array of ints, 7 ints wide. a fieldPath value is
+// 6 ints wide. a history value encodes the number of valid entries in its
+// first position. e.g., this:
+// [0 0 0 0 0 0 0]
+// would indicate the selection [0]
+// [0 4 0 0 0 0 0]
+// would indicate the selection [4]
+// [1 4 2 0 0 0 0]
+// would indicate the selection [4 2]
+func (f *fieldPath) keep() {
+	f.hlast++
+	f.history[f.hlast][0] = f.last
+	for i := 0; i <= f.last; i++ {
+		f.history[f.hlast][i+1] = f.vals[i]
+	}
+}
+
 func (f *fieldPath) getField(class *Class) *Field {
 	if f.last > 0 {
 		for i := 0; i < f.last; i++ {