[constraints] provide default ctor

frackit/entitynetwork/constraints.hh

@@ -27,6 +27,7 @@
 #include <stdexcept>
 #include <variant>
 #include <vector>
+#include <type_traits>
 
 #include <frackit/distance/distance.hh>
 #include <frackit/magnitude/magnitude.hh>
@@ -88,6 +89,17 @@ public:
     //! Exort the engine used for angle computations
     using AngleComputationEngine = AE;
 
+    /*!
+     * \brief Default constructor.
+     * \note This is only available if the engines are default constructible
+     */
+    EntityNetworkConstraints()
+    {
+        static_assert(std::is_default_constructible<AE>::value,
+                      "Angle computation engine not default constructible. "
+                      "Use constructor taking the engines as arguments instead");
+    }
+
     /*!
      * \brief The constructor.
      * \param angleEngine An instance of the engine used for angle computations.

test/entitynetwork/test_constraints_disk.cc

@@ -22,7 +22,7 @@ int main()
     const Vector e3(0.0, 0.0, 1.0);
 
     // Define constraints
-    auto constraints = Frackit::makeDefaultConstraints<ctype>();
+    Frackit::EntityNetworkConstraints<ctype> constraints;
     constraints.setMinDistance(0.1);
     constraints.setMinIntersectingAngle(M_PI/4.0);
     constraints.setMinIntersectionMagnitude(0.05);