internal/gocore/region.go
func (r region) SliceLen() int64 {
	if r.typ.Kind != KindSlice {
		panic("can't len a non-slice")
	}
	return r.p.proc.ReadInt(r.a.Add(r.p.proc.PtrSize()))
}
func (r region) SliceLen() int64 {
	if r.typ.Kind != KindSlice {
		panic("can't len a non-slice")
	}
	return r.p.proc.ReadInt(r.a.Add(r.p.proc.PtrSize()))
}
// SliceLen returns the length of a slice. r must contain a slice.