wireType     map[typeId]*wireType                    // map from remote ID to local description
	decoderCache map[reflect.Type]map[typeId]**decEngine // cache of compiled engines
	ignorerCache map[typeId]**decEngine                  // ditto for ignored objects
	freeList     *decoderState                           // list of free decoderStates; avoids reallocation

func (dec *Decoder) getIgnoreEnginePtr(wireId typeId) (enginePtr **decEngine, err error) {
	var ok bool
	if enginePtr, ok = dec.ignorerCache[wireId]; !ok {
		// To handle recursive types, mark this engine as underway before compiling.
		enginePtr = new(*decEngine)
		dec.ignorerCache[wireId] = enginePtr
		wire := dec.wireType[wireId]
		if wire != nil && wire.StructT != nil {