From 4bd9eeb8ee81d57072c874c2a7b2d1b758abb6ce Mon Sep 17 00:00:00 2001
From: Ichthyostega <prg@ichthyostega.de>
Date: Sun, 6 Oct 2013 18:50:53 +0200
Subject: [PATCH] bughunt: re-create the whole 2nd layer with a configurable
 product type --> HIT

Now we've reprduced the problematic situation in isolation
---
 research/clang-static-init-1.cpp |  14 +---
 research/clang-static-init-2.cpp |  24 ++++---
 research/clang-static-init.hpp   | 106 +++++++++++++++++++++++++++----
 3 files changed, 109 insertions(+), 35 deletions(-)

diff --git a/research/clang-static-init-1.cpp b/research/clang-static-init-1.cpp
index 7170aa999..020f469b3 100644
--- a/research/clang-static-init-1.cpp
+++ b/research/clang-static-init-1.cpp
@@ -1,26 +1,18 @@
 
 #include "clang-static-init.hpp"
 
-#include <iostream>
 
 
-using std::cout;
-using std::endl;
-
-using namespace test;
-
 int
 main (int, char**)
   {
-    cout <<  "\n.gulp.\n";
+    cout <<  "\nStart Testcase: invoking two instances of the configurable singleton factory...\n";
     
-    Subject& ref1 = fab.get();
-    Subject& sub2 = test::fabricate();
+    test::Subject& ref1 = test::fab.get();
+    test::Subject& sub2 = test::fabricate();
     
     cout << "sub1="<< &ref1 << " sub2="<< &sub2 <<"\n";
     
     
     return 0;
   }
-
-
diff --git a/research/clang-static-init-2.cpp b/research/clang-static-init-2.cpp
index 80cba771e..c23468837 100644
--- a/research/clang-static-init-2.cpp
+++ b/research/clang-static-init-2.cpp
@@ -1,29 +1,33 @@
 
 #include "clang-static-init.hpp"
 
-#include <iostream>
-
-using std::cout;
-using std::endl;
 
 
 namespace test {
   
   
-  int Subject::cnt = 0;
+  int Subject::creationCount = 0;
   
   Subject::Subject()
     {
-      ++cnt;
-      std::cout << "Subject("<<cnt<<")\n";
+      ++creationCount;
+      std::cout << "Subject("<<creationCount<<")\n";
     }
-   
+  
+  
   
   namespace {
-      //
+      TypeInfo<Subject> shall_build_a_Subject_instance;
   }
   
-  AccessPoint fab;
+  /**
+   * instance of the singleton factory
+   * @note especially for this example we're using just \em one
+   *       shared instance of the factory.
+   *       Yet still, the two (inlined) calls to the get() function
+   *       access different addresses for the embedded singleton instance
+   */
+  AccessPoint fab(shall_build_a_Subject_instance);
   
   
   Subject&
diff --git a/research/clang-static-init.hpp b/research/clang-static-init.hpp
index f0694fd6b..6597e8b05 100644
--- a/research/clang-static-init.hpp
+++ b/research/clang-static-init.hpp
@@ -1,54 +1,132 @@
 
+#include <iostream>
+
+using std::cout;
+
 
 namespace test {
-
-  template<typename T
-          ,template <class> class Fac
+  
+  
+  
+  /* === Layer-1: a singleton factory based on a templated static variable === */
+  
+  template<typename I                     ///< Interface of the product type
+          ,template <class> class Fac     ///< Policy: actual factory to create the instance
           >
   struct Holder
     {
-      static T* instance;
+      static I* instance;
       
-      T&
+      I&
       get()
         {
           if (!instance)
             {
-              instance = Fac<T>::create();
+              cout << "Singleton Factory: invoke Fabrication ---> instance="<<&instance<<"...\n";
+              
+              instance = Fac<I>::create();
             }
           return *instance;
         }
     };
   
-  
-  template<typename T
+  /**
+   * allocate storage for the per-type shared
+   * (static) variable to hold the singleton instance
+   */
+  template<typename I
           ,template <class> class F
           >
-  T* Holder<T,F>::instance;
+  I* Holder<I,F>::instance;
   
   
   
-  template<typename T>
+  
+  template<typename C>
   struct Factory
     {
-      static T*
+      static C*
       create()
         {
-          return new T();
+          return new C();
         }
     };
   
   
   
+  
+  
+  /* === Layer-2: configurable product type === */
+  
+  template<typename I>
+  struct Adapter
+    {
+      typedef I* FactoryFunction (void);
+      
+      static FactoryFunction* factoryFunction;
+      
+      
+      template<typename C>
+      static I*
+      concreteFactoryFunction()
+        {
+          return static_cast<I*> (Factory<C>::create());
+        }
+      
+      
+      template<typename X>
+      struct AdaptedConfigurableFactory
+        {
+          static X*
+          create()
+            {
+              return (*factoryFunction)();
+            }
+        };
+    };
+  
+  /** storage for the per-type shared function pointer to the concrete factory */
+  template<typename I>
+  typename Adapter<I>::FactoryFunction*  Adapter<I>::factoryFunction;
+  
+  
+  
+  template<typename C>
+  struct TypeInfo { };
+  
+  
+  
+  /**
+   * Singleton factory with the ability to configure the actual product type C
+   * only at the \em definition site. Users get to see only the interface type T
+   */
+  template<typename T>
+  struct ConfigurableHolder
+    : Holder<T, Adapter<T>::template AdaptedConfigurableFactory>
+    {
+      /** define the actual product type */
+      template<typename C>
+      ConfigurableHolder (TypeInfo<C>)
+        {
+          Adapter<T>::factoryFunction = &Adapter<T>::template concreteFactoryFunction<C>;
+        }
+    };
+  
+  
+  
+  
+  
+  /* === Actual usage: Test case fabricating Subject instances === */
+  
   struct Subject
     {
-      static int cnt;
+      static int creationCount;
       
       Subject();
       
     };
   
-  typedef Holder<Subject,Factory> AccessPoint;
+  typedef ConfigurableHolder<Subject> AccessPoint;
   
   extern AccessPoint fab;