refactor(poly): updated header guards to pragma once

src/poly/solver/public/polySolver.h

@@ -1,5 +1,4 @@
-#ifndef POLYSOLVER_H
-#define POLYSOLVER_H
+#pragma once
 
 #include "mfem.hpp"
 #include <memory>
@@ -21,8 +20,8 @@ namespace laneEmden {
 
 // Struct to persist lifetime of the linear and nonlinear solvers
 struct solverBundle {
-    mfem::GMRESSolver solver;
-    mfem::NewtonSolver newton;
+    mfem::GMRESSolver solver; // Must be first so it lives longer than the newton solver
+    mfem::NewtonSolver newton; // Must be second so that when it is destroyed the solver is still alive preventing a double delete
 };
 
 class PolySolver {
@@ -32,10 +31,10 @@ public: // Public methods
 
     void solve() const;
 
-    double getN() { return m_polytropicIndex; }
-    double getOrder() { return m_feOrder; }
-    mfem::Mesh* getMesh() { return m_mesh.get(); }
-    mfem::GridFunction& getSolution() { return *m_theta; }
+    double getN() const { return m_polytropicIndex; }
+    double getOrder() const { return m_feOrder; }
+    mfem::Mesh* getMesh() const { return m_mesh.get(); }
+    mfem::GridFunction& getSolution() const { return *m_theta; }
 
 private: // Private Attributes
     Config& m_config = Config::getInstance();
@@ -70,6 +69,4 @@ private: // Private methods
     void LoadSolverUserParams(double &newtonRelTol, double &newtonAbsTol, int &newtonMaxIter, int &newtonPrintLevel,
                               double &gmresRelTol, double &gmresAbsTol, int &gmresMaxIter, int &gmresPrintLevel) const;
 
-};
-
-#endif // POLYSOLVER_H
+};