inference/support/util.hh: use rvalue references

src/graph/inference/support/util.hh

@@ -87,7 +87,7 @@ T log_sum(T a, T b)
 }
 
 template <class Vec, class PosMap, class Val>
-void remove_element(Vec& vec, PosMap& pos, Val val)
+void remove_element(Vec& vec, PosMap& pos, Val&& val)
 {
     auto& back = vec.back();
     auto& j = pos[back];
@@ -98,14 +98,14 @@ void remove_element(Vec& vec, PosMap& pos, Val val)
 }
 
 template <class Vec, class PosMap, class Val>
-void add_element(Vec& vec, PosMap& pos, Val val)
+void add_element(Vec& vec, PosMap& pos, Val&& val)
 {
     pos[val] = vec.size();
     vec.push_back(val);
 }
 
 template <class Vec, class PosMap, class Val>
-bool has_element(Vec& vec, PosMap& pos, Val val)
+bool has_element(Vec& vec, PosMap& pos, Val&& val)
 {
     size_t i = pos[val];
     return (i < vec.size() && vec[i] == val);