Disable get_water_flux_reconstructed at compile-time

Use enable_if instead of throwing at run-time

dune/dorie/model/richards/richards.hh

@@ -542,60 +542,57 @@ public:
 	 *
 	 * @return     Pointer to a (reconstructed) water flux grid function
 	 */
-	std::shared_ptr<const GFFluxReconstruction> get_water_flux_reconstructed(ConstState state) const
+	template<bool enabled=enable_rt_engine>
+	std::enable_if_t<enabled, std::shared_ptr<const GFFluxReconstruction>>
+	get_water_flux_reconstructed(ConstState state) const
 	{
 		std::shared_ptr<GFFluxReconstruction> gf_ptr;
 
 		auto& cache = cache_water_flux_gf_rt;
 
-		if constexpr (enable_rt_engine)
+		if (state.grid_function_space != gfs
+			or state.coefficients != u
+			or state.time != current_time())
 		{
+			// if state is different to current state, create flux from zero
 
-			if (state.grid_function_space != gfs or 
-					state.coefficients != u or
-					state.time != current_time())
-			{
-				// if state is different to current state, create flux from zero
-
-				gf_ptr = std::make_unique<GFFluxReconstruction>(
-      									this->_log,gv,inifile.sub("fluxReconstruction"));
-
-	      assert(fboundary);
-	      assert(fparam);
-	      assert(slop);
-	      
-	      slop->setTime(state.time);
-
-	      // update it with the state
-	      gf_ptr->update(*(state.coefficients),
-	      							 *(state.grid_function_space),
-	      							 *slop);
-
-	      slop->setTime(current_time());
-			} else if (not cache) {
-				// if state is equal to current state, use cache.
-
-      	cache = std::make_unique<GFFluxReconstruction>(
-      									this->_log,gv,inifile.sub("fluxReconstruction"));
-
-	      assert(fboundary);
-	      assert(fparam);
-	      assert(slop);
-	      
-	      // update it with current state
-	      cache->update(*u,*gfs,*slop);
-
-	      gf_ptr = cache;
-	    } else {
-	    	gf_ptr = cache;
-	    }
-
-		} else {
-			DUNE_THROW(NotImplemented, 
-				"Flux reconstruction is not implemented for the selected "
-				<< "configuration");
+			gf_ptr = std::make_unique<GFFluxReconstruction>(
+									this->_log,gv,inifile.sub("fluxReconstruction"));
+
+			assert(fboundary);
+			assert(fparam);
+			assert(slop);
+
+			slop->setTime(state.time);
+
+			// update it with the state
+			gf_ptr->update(*(state.coefficients),
+										*(state.grid_function_space),
+										*slop);
+
+			slop->setTime(current_time());
+		}
+
+		// if state is equal to current state, use cache.
+		else if (not cache) {
+
+			cache = std::make_unique<GFFluxReconstruction>(
+									this->_log,gv,inifile.sub("fluxReconstruction"));
+
+			assert(fboundary);
+			assert(fparam);
+			assert(slop);
+
+			// update it with current state
+			cache->update(*u,*gfs,*slop);
+
+			gf_ptr = cache;
 		}
-		
+
+		else {
+			gf_ptr = cache;
+		}
+
 		return gf_ptr;
 	}
 
@@ -604,10 +601,12 @@ public:
 	 *
 	 * @return     Pointer to a (reconstructed) water flux grid function
 	 */
-	std::shared_ptr<const GFFluxReconstruction> get_water_flux_reconstructed() const
+	template<bool enabled=enable_rt_engine>
+	std::enable_if_t<enabled, std::shared_ptr<const GFFluxReconstruction>>
+	get_water_flux_reconstructed() const
 	{
 		return get_water_flux_reconstructed(current_state());
-	} 
+	}
 
 protected: