diff --git a/protothread.h b/protothread.h
index a1a533e..28d3bb7 100644
--- a/protothread.h
+++ b/protothread.h
@@ -88,7 +88,9 @@ class Protothread
 public:
     // Construct a new protothread that will start from the beginning
     // of its Run() function.
-    Protothread() : _ptLine(0) { }
+    Protothread() = default;
+
+    virtual ~Protothread() = default;
 
     // Restart protothread.
     void Restart() { _ptLine = 0; }
@@ -100,7 +102,7 @@ class Protothread
 
     // Return true if the protothread is running or waiting, false if it has
     // ended or exited.
-    bool IsRunning() { return _ptLine != LineNumberInvalid; }
+    bool IsRunning() const { return _ptLine != LineNumberInvalid; }
 
     // Run next part of protothread or return immediately if it's still
     // waiting. Return true if protothread is still running, false if it
@@ -110,14 +112,14 @@ class Protothread
 protected:
     // Used to store a protothread's position (what Dunkels calls a
     // "local continuation").
-    typedef unsigned short LineNumber;
+    using LineNumber = unsigned short;
 
     // An invalid line number, used to mark the protothread has ended.
     static const LineNumber LineNumberInvalid = (LineNumber)(-1);
 
     // Stores the protothread's position (by storing the line number of
     // the last PT_WAIT, which is then switched on at the next Run).
-    LineNumber _ptLine;
+    LineNumber _ptLine = 0;
 };
 
 // Declare start of protothread (use at start of Run() implementation).
diff --git a/simcpp.cpp b/simcpp.cpp
index cd40a1d..7dca500 100644
--- a/simcpp.cpp
+++ b/simcpp.cpp
@@ -9,7 +9,7 @@ namespace simcpp {
 
 SimulationPtr Simulation::create() { return std::make_shared<Simulation>(); }
 
-void Simulation::run_process(ProcessPtr process, simtime delay /* = 0.0 */) {
+void Simulation::run_process(const ProcessPtr& process, simtime delay /* = 0.0 */) {
   auto event = this->event();
   event->add_handler(process);
   event->trigger(delay);
@@ -23,7 +23,7 @@ EventPtr Simulation::timeout(simtime delay) {
 
 EventPtr Simulation::any_of(std::initializer_list<EventPtr> events) {
   int n = 1;
-  for (auto &event : events) {
+  for (const auto &event : events) {
     if (event->is_triggered()) {
       n = 0;
       break;
@@ -39,7 +39,7 @@ EventPtr Simulation::any_of(std::initializer_list<EventPtr> events) {
 
 EventPtr Simulation::all_of(std::initializer_list<EventPtr> events) {
   int n = 0;
-  for (auto &event : events) {
+  for (const auto &event : events) {
     if (!event->is_triggered()) {
       ++n;
     }
@@ -52,7 +52,7 @@ EventPtr Simulation::all_of(std::initializer_list<EventPtr> events) {
   return process;
 }
 
-void Simulation::schedule(EventPtr event, simtime delay /* = 0.0 */) {
+void Simulation::schedule(const EventPtr& event, simtime delay /* = 0.0 */) {
   queued_events.emplace(now + delay, next_id, event);
   ++next_id;
 }
@@ -78,7 +78,7 @@ void Simulation::advance_by(simtime duration) {
   now = target;
 }
 
-bool Simulation::advance_to(EventPtr event) {
+bool Simulation::advance_to(const EventPtr& event) {
   while (event->is_pending() && has_next()) {
     step();
   }
@@ -87,19 +87,18 @@ bool Simulation::advance_to(EventPtr event) {
 }
 
 void Simulation::run() {
-  while (step()) {
-  }
+    while (step());
 }
 
-simtime Simulation::get_now() { return now; }
+simtime Simulation::get_now() const { return now; }
 
-bool Simulation::has_next() { return !queued_events.empty(); }
+bool Simulation::has_next() const { return !queued_events.empty(); }
 
-simtime Simulation::peek_next_time() { return queued_events.top().time; }
+simtime Simulation::peek_next_time() const { return queued_events.top().time; }
 
 /* Simulation::QueuedEvent */
 
-Simulation::QueuedEvent::QueuedEvent(simtime time, size_t id, EventPtr event)
+Simulation::QueuedEvent::QueuedEvent(simtime time, size_t id, const EventPtr& event)
     : time(time), id(id), event(event) {}
 
 bool Simulation::QueuedEvent::operator<(const QueuedEvent &other) const {
@@ -112,15 +111,15 @@ bool Simulation::QueuedEvent::operator<(const QueuedEvent &other) const {
 
 /* Event */
 
-Event::Event(SimulationPtr sim) : sim(sim) {}
+Event::Event(const SimulationPtr& sim) : sim(sim) {}
 
-bool Event::add_handler(ProcessPtr process) {
+bool Event::add_handler(const ProcessPtr& process) {
   // Handler takes an additional EventPtr arg, but this is ignored by the
   // bound function.
   return add_handler(std::bind(&Process::resume, process));
 }
 
-bool Event::add_handler(Handler handler) {
+bool Event::add_handler(const Handler& handler) {
   if (is_triggered()) {
     return false;
   }
@@ -167,30 +166,30 @@ void Event::process() {
 
   state = State::Processed;
 
-  for (auto &handler : handlers) {
+  for (const auto& handler : handlers) {
     handler(shared_from_this());
   }
 
   handlers.clear();
 }
 
-bool Event::is_pending() { return state == State::Pending; }
+bool Event::is_pending() const { return state == State::Pending; }
 
-bool Event::is_triggered() {
+bool Event::is_triggered() const {
   return state == State::Triggered || state == State::Processed;
 }
 
-bool Event::is_processed() { return state == State::Processed; }
+bool Event::is_processed() const { return state == State::Processed; }
 
-bool Event::is_aborted() { return state == State::Aborted; }
+bool Event::is_aborted() const { return state == State::Aborted; }
 
-Event::State Event::get_state() { return state; }
+Event::State Event::get_state() const { return state; }
 
 void Event::Aborted() {}
 
 /* Process */
 
-Process::Process(SimulationPtr sim) : Event(sim), Protothread() {}
+Process::Process(const SimulationPtr& sim) : Event(sim), Protothread() {}
 
 void Process::resume() {
   // Is the process already finished?
@@ -213,7 +212,7 @@ ProcessPtr Process::shared_from_this() {
 
 /* Condition */
 
-Condition::Condition(SimulationPtr sim, int n) : Process(sim), n(n) {}
+Condition::Condition(const SimulationPtr& sim, int n) : Process(sim), n(n) {}
 
 bool Condition::Run() {
   PT_BEGIN();
diff --git a/simcpp.h b/simcpp.h
index 751b8de..450b847 100644
--- a/simcpp.h
+++ b/simcpp.h
@@ -92,7 +92,7 @@ class Simulation : public std::enable_shared_from_this<Simulation> {
    * @param process Process to be run.
    * @param delay Delay after which to run the process.
    */
-  void run_process(ProcessPtr process, simtime delay = 0.0);
+  void run_process(const ProcessPtr& process, simtime delay = 0.0);
 
   /**
    * Construct an event.
@@ -142,7 +142,7 @@ class Simulation : public std::enable_shared_from_this<Simulation> {
    * @param event Event instance.
    * @param delay Delay after which the event is processed.
    */
-  void schedule(EventPtr event, simtime delay = 0.0);
+  void schedule(const EventPtr& event, simtime delay = 0.0);
 
   /**
    * Process the next scheduled event.
@@ -165,19 +165,19 @@ class Simulation : public std::enable_shared_from_this<Simulation> {
    * @return Whether the event was triggered. If no scheduled events are left or
    * the event is aborted, this is not the case.
    */
-  bool advance_to(EventPtr event);
+  bool advance_to(const EventPtr& event);
 
   /// Run the simulation until no scheduled events are left.
   void run();
 
   /// @return Current simulation time.
-  simtime get_now();
+  simtime get_now() const;
 
   /// @return Whether a scheduled event is left.
-  bool has_next();
+  bool has_next() const;
 
   /// @return Time at which the next event is scheduled.
-  simtime peek_next_time();
+  simtime peek_next_time() const;
 
 private:
   class QueuedEvent {
@@ -186,7 +186,7 @@ class Simulation : public std::enable_shared_from_this<Simulation> {
     size_t id;
     EventPtr event;
 
-    QueuedEvent(simtime time, size_t id, EventPtr event);
+    QueuedEvent(simtime time, size_t id, const EventPtr& event);
 
     bool operator<(const QueuedEvent &other) const;
   };
@@ -221,7 +221,7 @@ class Event : public std::enable_shared_from_this<Event> {
    *
    * @param sim Simulation instance.
    */
-  explicit Event(SimulationPtr sim);
+  explicit Event(const SimulationPtr& sim);
 
   /**
    * Add the resume method of a process as an handler of the event.
@@ -233,7 +233,7 @@ class Event : public std::enable_shared_from_this<Event> {
    * @param process The process to resume when the event is processed.
    * @return Whether the event was not already triggered.
    */
-  bool add_handler(ProcessPtr process);
+  bool add_handler(const ProcessPtr& process);
 
   /**
    * Add the callback as an handler of the event.
@@ -244,7 +244,7 @@ class Event : public std::enable_shared_from_this<Event> {
    * receives the event instance as an argument.
    * @return Whether the event was not already triggered.
    */
-  bool add_handler(Handler handler);
+  bool add_handler(const Handler& handler);
 
   /**
    * Trigger the event with a delay.
@@ -274,22 +274,22 @@ class Event : public std::enable_shared_from_this<Event> {
   void process();
 
   /// @return Whether the event is pending.
-  bool is_pending();
+  bool is_pending() const;
 
   /**
    * @return Whether the event is triggered. Also true if the event is
    * processed.
    */
-  bool is_triggered();
+  bool is_triggered() const;
 
   /// @return Whether the event is aborted.
-  bool is_aborted();
+  bool is_aborted() const;
 
   /// @return Whether the event is processed.
-  bool is_processed();
+  bool is_processed() const;
 
   /// @return Whether the event is pending.
-  State get_state();
+  State get_state() const;
 
   /// Called when the event is aborted.
   virtual void Aborted();
@@ -316,7 +316,7 @@ class Process : public Event, public Protothread {
    *
    * @param sim Simulation instance.
    */
-  explicit Process(SimulationPtr sim);
+  explicit Process(const SimulationPtr& sim);
 
   /**
    * Resumes the process.
@@ -339,7 +339,7 @@ class Condition : public Process {
    * @param sim Simulation instance.
    * @param n Number of times the process must be resumed before it finishes.
    */
-  Condition(SimulationPtr sim, int n);
+  Condition(const SimulationPtr& sim, int n);
 
   /**
    * Wait for the given number of resumes and then finish.
diff --git a/simobj.h b/simobj.h
index af7c7e3..e0211f8 100644
--- a/simobj.h
+++ b/simobj.h
@@ -1,3 +1,6 @@
+#ifndef SIMOBJ_H_
+#define SIMOBJ_H_
+
 #include "simcpp.h"
 
 #define OBSERVABLE_PROPERTY(TYP, NAM, VAL)                                     \
@@ -5,18 +8,27 @@ private:                                                                       \
   TYP NAM = VAL;                                                               \
                                                                                \
 public:                                                                        \
-  shared_ptr<Event> NAM##_event = std::make_shared<Event>(env);                \
-  TYP get_##NAM() { return this->NAM; }                                        \
+  simcpp::EventPtr NAM##_event{std::make_shared<simcpp::Event>(env)};          \
+  TYP get_##NAM() const { return this->NAM; }                                  \
   void set_##NAM(TYP v) {                                                      \
     this->NAM = v;                                                             \
     this->env->schedule(this->NAM##_event);                                    \
-    this->NAM##_event = std::make_shared<Event>(env);                          \
+    this->NAM##_event = std::make_shared<simcpp::Event>(env);                  \
   }
 
+
+namespace simcpp {
+
 class EnvObj {
 protected:
-  shared_ptr<Simulation> env;
+    SimulationPtr env;
 
 public:
-  EnvObj(shared_ptr<Simulation> s) : env(s) {}
+    explicit EnvObj(const SimulationPtr& s) : env(s) {}
+    virtual ~EnvObj() = default;
 };
+
+}
+
+
+#endif