specs_odr_guard

Author: rwgk

caster_odr_specs_odr_guard/car.cc

@@ -0,0 +1,21 @@
+#include "engine.h"
+
+namespace vehicles {
+
+struct vehicle {};
+
+struct car_specs {
+  static constexpr unsigned unique_id = 10;
+  int power() const { return 100; }
+};
+
+}  // namespace vehicles
+
+namespace engine {
+
+template <>
+struct specs<vehicles::vehicle> : vehicles::car_specs {};
+
+}  // namespace engine
+
+int car_power() { return engine::power<vehicles::vehicle>(); }

caster_odr_specs_odr_guard/compile_and_run.bat

@@ -0,0 +1,4 @@
+cl car.cc truck.cc vehicle_specs.cc /Fe"show.exe"
+.\show
+cl truck.cc car.cc vehicle_specs.cc /Fe"show.exe"
+.\show

caster_odr_specs_odr_guard/compile_and_run.sh

@@ -0,0 +1,5 @@
+set -e
+set -x
+clang++ -std=c++11 car.cc truck.cc vehicle_specs.cc && ./a.out
+clang++ -std=c++11 truck.cc car.cc vehicle_specs.cc && ./a.out
+rm a.out

caster_odr_specs_odr_guard/engine.h

@@ -0,0 +1,42 @@
+#pragma once
+
+#include <stdio.h>
+
+#include <typeinfo>
+
+namespace engine {
+
+template <typename T>
+struct specs {
+  static constexpr unsigned unique_id = 0;
+  int power() const { return 0; }
+};
+
+namespace {
+
+template <typename T>
+struct specs_odr_guard : specs<T> {
+  static int translation_unit_local;
+};
+
+template <typename T>
+int specs_odr_guard<T>::translation_unit_local = []() {
+  fprintf(stdout, "MAKE_SPECS_ODR_GUARD %s %u\n", typeid(T).name(),
+          specs<T>::unique_id);
+  fflush(stdout);
+  return 0;
+}();
+
+}  // namespace
+
+template <typename T>
+using make_specs = specs_odr_guard<T>;
+
+template <typename T>
+int power() {
+  if (make_specs<T>::translation_unit_local) {
+  }
+  return make_specs<T>().power();
+}
+
+}  // namespace engine

caster_odr_specs_odr_guard/truck.cc

@@ -0,0 +1,21 @@
+#include "engine.h"
+
+namespace vehicles {
+
+struct vehicle {};
+
+struct truck_specs {
+  static constexpr unsigned unique_id = 30;
+  int power() const { return 300; }
+};
+
+}  // namespace vehicles
+
+namespace engine {
+
+template <>
+struct specs<vehicles::vehicle> : vehicles::truck_specs {};
+
+}  // namespace engine
+
+int truck_power() { return engine::power<vehicles::vehicle>(); }

caster_odr_specs_odr_guard/vehicle_specs.cc

@@ -0,0 +1,13 @@
+#include <iostream>
+
+int car_power();
+int truck_power();
+
+int main() {
+  int pwr = 0;
+  pwr = car_power();
+  std::cout << "car   power: " << pwr << std::endl;
+  pwr = truck_power();
+  std::cout << "truck power: " << pwr << std::endl;
+  return 0;
+}