Add caster_odr_specs_scope experiment.

Another way to leverage unique_to_translation_unit.

Author: rwgk

caster_odr_specs_scope/car.cc

@@ -0,0 +1,28 @@
+#include "engine.h"
+
+namespace vehicles {
+
+struct vehicle;
+
+struct car_specs {
+  int power() const { return 100; }
+};
+
+}  // namespace vehicles
+
+namespace engine {
+
+template <>
+struct make_specs<vehicles::vehicle, unique_to_translation_unit>
+    : vehicles::car_specs {};
+
+template <>
+struct specs_scope<vehicles::vehicle, unique_to_translation_unit> {
+  using select = unique_to_translation_unit;
+};
+
+}  // namespace engine
+
+int car_power() {
+  return engine::power<vehicles::vehicle, engine::unique_to_translation_unit>();
+}

caster_odr_specs_scope/compile_and_run.bat

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

caster_odr_specs_scope/compile_and_run.sh

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

caster_odr_specs_scope/engine.h

@@ -0,0 +1,27 @@
+namespace engine {
+
+namespace {
+struct unique_to_translation_unit {};
+}  // namespace
+
+struct external_specs_scope {};
+
+template <typename T>
+struct specs {
+  int power() const { return 0; }
+};
+
+template <typename T, typename S>
+struct make_specs : specs<T> {};
+
+template <typename T, typename U>
+struct specs_scope {
+  using select = external_specs_scope;
+};
+
+template <typename T, typename U>
+int power() {
+  return make_specs<T, typename specs_scope<T, U>::select>().power();
+}
+
+}  // namespace engine

caster_odr_specs_scope/truck.cc

@@ -0,0 +1,28 @@
+#include "engine.h"
+
+namespace vehicles {
+
+struct vehicle;
+
+struct truck_specs {
+  int power() const { return 300; }
+};
+
+}  // namespace vehicles
+
+namespace engine {
+
+template <>
+struct make_specs<vehicles::vehicle, unique_to_translation_unit>
+    : vehicles::truck_specs {};
+
+template <>
+struct specs_scope<vehicles::vehicle, unique_to_translation_unit> {
+  using select = unique_to_translation_unit;
+};
+
+}  // namespace engine
+
+int truck_power() {
+  return engine::power<vehicles::vehicle, engine::unique_to_translation_unit>();
+}

caster_odr_specs_scope/unknown.cc

@@ -0,0 +1,11 @@
+#include "engine.h"
+
+namespace vehicles {
+
+struct vehicle;
+
+}
+
+int unknown_power() {
+  return engine::power<vehicles::vehicle, engine::unique_to_translation_unit>();
+}

caster_odr_specs_scope/vehicle_specs.cc

@@ -0,0 +1,12 @@
+#include <iostream>
+
+int unknown_power();
+int car_power();
+int truck_power();
+
+int main() {
+  std::cout << "unknown power:   " << unknown_power() << std::endl;
+  std::cout << "car     power:   " << car_power() << std::endl;
+  std::cout << "truck   power:   " << truck_power() << std::endl;
+  return 0;
+}