1 files changed, 6 insertions, 1 deletions
diff --git a/extractor/alignment.h b/extractor/alignment.h
index 290d6015..f7e79585 100644
--- a/extractor/alignment.h
+++ b/extractor/alignment.h
@@ -13,10 +13,15 @@ class Alignment {
  public:
   Alignment(const string& filename);
 
-  const vector<pair<int, int> >& GetLinks(int sentence_index) const;
+  virtual vector<pair<int, int> > GetLinks(int sentence_index) const;
 
   void WriteBinary(const fs::path& filepath);
 
+  virtual ~Alignment();
+
+ protected:
+  Alignment();
+
  private:
   vector<vector<pair<int, int> > > alignments;
 };