pair_criteria: require cut_off for EnergyCriterion (bug-sweep #29)

src/core/pair_criteria/EnergyCriterion.hpp

@@ -53,7 +53,11 @@ class EnergyCriterion : public PairCriterion {
   void set_cut_off(double c) { m_cut_off = c; }
 
 private:
-  double m_cut_off;
+  // in-class initializer: the user-provided ctor takes a System argument and
+  // thus direct-initializes the object (no value-initialization), so without
+  // this default m_cut_off would be indeterminate until set_cut_off runs
+  // (bug-sweep #29).
+  double m_cut_off = 0.0;
   System::System const &m_system;
 };
 } // namespace PairCriteria

src/script_interface/pair_criteria/EnergyCriterion.hpp

@@ -46,6 +46,15 @@ class EnergyCriterion : public PairCriterion {
           [this]() { return m_c->get_cut_off(); }}});
   }
 
+  void do_construct(VariantMap const &params) override {
+    // cut_off is the parameter that defines the criterion and has no
+    // meaningful default; enforce it as a required construction parameter.
+    // get_value throws "Parameter 'cut_off' is missing." when it is omitted,
+    // which prevents the core m_cut_off threshold from being left
+    // uninitialized (bug-sweep #29).
+    m_c->set_cut_off(get_value<double>(params, "cut_off"));
+  }
+
   std::shared_ptr<::PairCriteria::PairCriterion>
   pair_criterion() const override {
     return m_c;

testsuite/python/pair_criteria.py

@@ -93,6 +93,20 @@ def test_energy_crit_non_periodic(self):
         self.assertTrue(not ec.decide(self.p1, self.p2))
         self.assertTrue(not ec.decide(self.p1.id, self.p2.id))
 
+    def test_energy_crit_requires_cut_off(self):
+        # Regression test for bug-sweep #29: constructing an EnergyCriterion
+        # without the mandatory ``cut_off`` parameter must be rejected. On the
+        # unfixed code the omitted ``cut_off`` was silently accepted, leaving
+        # the core member ``m_cut_off`` uninitialized (the core object is
+        # direct-initialized via make_shared<EnergyCriterion>(system), so it is
+        # not value-initialized), and a subsequent get_params()/decide() read
+        # indeterminate memory. ``cut_off`` is THE parameter that defines the
+        # criterion, so it must be required, like the ``distance`` of
+        # DistanceCriterion.
+        with self.assertRaisesRegex(
+                RuntimeError, "Parameter 'cut_off' is missing."):
+            espressomd.pair_criteria.EnergyCriterion()
+
     def test_bond_crit(self):
         bt = 0
         bc = espressomd.pair_criteria.BondCriterion(bond_type=bt)