From 1f217e38f7507758da1d33d46e675e801621aa38 Mon Sep 17 00:00:00 2001
From: Michael Shepanski <michael@codesynthesis.com>
Date: Thu, 30 Oct 2014 15:21:32 +1100
Subject: Allow lambdas & std::functions as query factories with C++-98 builds
 of libodb

---
 odb/connection.cxx               |  11 +--
 odb/database.cxx                 |  32 ++++++++
 odb/database.hxx                 |  38 ++++++---
 odb/database.ixx                 |  27 +------
 odb/details/function-wrapper.hxx |  83 ++++++++++++++++++++
 odb/details/function-wrapper.ixx |  47 +++++++++++
 odb/details/function-wrapper.txx |  87 +++++++++++++++++++++
 odb/schema-catalog.cxx           |  20 +++--
 odb/schema-catalog.hxx           | 164 ++++++++++++++++++++++++++++++++++-----
 9 files changed, 441 insertions(+), 68 deletions(-)
 create mode 100644 odb/details/function-wrapper.hxx
 create mode 100644 odb/details/function-wrapper.ixx
 create mode 100644 odb/details/function-wrapper.txx

diff --git a/odb/connection.cxx b/odb/connection.cxx
index 4319f9f..14e89e2 100644
--- a/odb/connection.cxx
+++ b/odb/connection.cxx
@@ -96,16 +96,11 @@ namespace odb
 
     if (i == prepared_map_.end ())
     {
-      // See if there is a factory.
+      // Use a factory, if there is one.
       //
-      database_type::query_factory_type f (
-        database_.lookup_query_factory (name));
-
-      if (f)
-      {
-        f (name, const_cast<connection&> (*this));
+      if (database_.call_query_factory (name,
+                                        const_cast<connection&> (*this)))
         i = prepared_map_.find (name);
-      }
     }
 
     if (i == prepared_map_.end ())
diff --git a/odb/database.cxx b/odb/database.cxx
index 5578abd..0279acd 100644
--- a/odb/database.cxx
+++ b/odb/database.cxx
@@ -49,4 +49,36 @@ namespace odb
       schema_version_seq_++;
     }
   }
+
+  bool database::
+  call_query_factory (const char* name, connection_type& c) const
+  {
+    query_factory_map::const_iterator i (query_factory_map_.find (name));
+
+    if (i == query_factory_map_.end ())
+      i = query_factory_map_.find (""); // Wildcard factory.
+
+    if (i == query_factory_map_.end ())
+      return false;
+
+    const query_factory_wrapper& fw (i->second);
+    if (fw.std_function == 0)
+      fw.function (name, c);
+    else
+    {
+      typedef void (*caller) (const void*, const char*, connection_type&);
+      reinterpret_cast<caller> (fw.function) (fw.std_function, name, c);
+    }
+
+    return true;
+  }
+
+  void database::
+  query_factory (const char* name, query_factory_wrapper w)
+  {
+    if (w)
+      query_factory_map_[name] = w; // Destructive copy assignment (move).
+    else
+      query_factory_map_.erase (name);
+  }
 }
diff --git a/odb/database.hxx b/odb/database.hxx
index 91d8e94..4e59aaf 100644
--- a/odb/database.hxx
+++ b/odb/database.hxx
@@ -15,7 +15,9 @@
 #include <cstddef> // std::size_t
 
 #ifdef ODB_CXX11
-#  include <functional> // std::function
+#  include <utility>     // std::move
+#  include <functional>  // std::function
+#  include <type_traits> // std::enable_if, std::is_convertible
 #endif
 
 #include <odb/traits.hxx>
@@ -30,6 +32,7 @@
 #include <odb/details/export.hxx>
 #include <odb/details/mutex.hxx>
 #include <odb/details/c-string.hxx>
+#include <odb/details/function-wrapper.hxx>
 
 namespace odb
 {
@@ -44,7 +47,6 @@ namespace odb
     // Object persistence API.
     //
   public:
-
     // Make the object persistent.
     //
     template <typename T>
@@ -281,19 +283,31 @@ namespace odb
   public:
     typedef odb::connection connection_type;
 
-#ifdef ODB_CXX11
-    typedef
-    std::function<void (const char*, connection_type&)>
-    query_factory_type;
+    typedef void query_factory_type (const char* name, connection_type&);
+    typedef query_factory_type* query_factory_ptr;
+    typedef details::function_wrapper<
+      query_factory_type> query_factory_wrapper;
+
+#ifndef ODB_CXX11
+    void
+    query_factory (const char* name, query_factory_ptr);
 #else
-    typedef void (*query_factory_type) (const char*, connection_type&);
+    template <typename F>
+    typename std::enable_if<
+      std::is_convertible<
+      F, std::function<query_factory_type>>::value, void>::type
+    query_factory (const char* name, F f)
+    {
+      query_factory (name, query_factory_wrapper (std::move (f)));
+    }
 #endif
 
-    void
-    query_factory (const char* name, query_factory_type);
+    bool
+    call_query_factory (const char* name, connection_type&) const;
 
-    query_factory_type
-    lookup_query_factory (const char* name) const;
+  private:
+    void
+    query_factory (const char* name, query_factory_wrapper);
 
     // Native database statement execution.
     //
@@ -480,7 +494,7 @@ namespace odb
 
   protected:
     typedef
-    std::map<const char*, query_factory_type, details::c_string_comparator>
+    std::map<const char*, query_factory_wrapper, details::c_string_comparator>
     query_factory_map;
 
     typedef std::map<std::string, schema_version_info> schema_version_map;
diff --git a/odb/database.ixx b/odb/database.ixx
index a15bb7d..6cfbeec 100644
--- a/odb/database.ixx
+++ b/odb/database.ixx
@@ -3,7 +3,6 @@
 // license   : GNU GPL v2; see accompanying LICENSE file
 
 #include <cstring> // std::strlen()
-#include <utility> // std::move
 
 #include <odb/transaction.hxx>
 
@@ -65,31 +64,13 @@ namespace odb
     return connection_ptr (connection_ ());
   }
 
+#ifndef ODB_CXX11
   inline void database::
-  query_factory (const char* name, query_factory_type f)
+  query_factory (const char* name, query_factory_ptr f)
   {
-    if (f)
-#ifdef ODB_CXX11
-      query_factory_map_[name] = std::move (f);
-#else
-      query_factory_map_[name] = f;
-#endif
-    else
-      query_factory_map_.erase (name);
-  }
-
-  inline database::query_factory_type database::
-  lookup_query_factory (const char* name) const
-  {
-    query_factory_map::const_iterator i (query_factory_map_.find (name));
-
-    if (i == query_factory_map_.end ())
-      i = query_factory_map_.find (""); // Wildcard factory.
-
-    return i != query_factory_map_.end ()
-      ? i->second
-      : database::query_factory_type ();
+    query_factory (name, query_factory_wrapper (f));
   }
+#endif
 
   inline void database::
   tracer (tracer_type& t)
diff --git a/odb/details/function-wrapper.hxx b/odb/details/function-wrapper.hxx
new file mode 100644
index 0000000..5615fca
--- /dev/null
+++ b/odb/details/function-wrapper.hxx
@@ -0,0 +1,83 @@
+// file      : odb/details/function-wrapper.hxx
+// copyright : Copyright (c) 2009-2014 Code Synthesis Tools CC
+// license   : GNU GPL v2; see accompanying LICENSE file
+
+#ifndef ODB_DETAILS_FUNCTION_WRAPPER_HXX
+#define ODB_DETAILS_FUNCTION_WRAPPER_HXX
+
+#include <odb/pre.hxx>
+
+#include <odb/details/config.hxx> // ODB_CXX11
+
+#ifdef ODB_CXX11
+#  include <functional>  // std::function
+#  include <type_traits> // std::enable_if, std::is_convertible
+#endif
+
+namespace odb
+{
+  namespace details
+  {
+    // Low-level 'callable object' wrapper similar to std::function but
+    // that works in both C++98 and 11. In particular, the call site can
+    // be compiled in C++98 and the registration site in C++11 and it
+    // will work.
+    //
+    template <typename F>
+    struct function_wrapper
+    {
+      ~function_wrapper ();
+
+      explicit
+      function_wrapper (F* = 0);
+
+#ifdef ODB_CXX11
+      typedef typename std::function<F> std_function_type;
+
+      // This overload accepts lambdas and std::functions, but when the
+      // argument is convertible to F*, then we disable it in favor of the
+      // other overload (above), which is more efficient.
+      //
+      // Subtlety alert: if you're thinking of changing this to accept a
+      // std::function<F> argument, stop. That creates an overload ambiguity
+      // when the actual parameter is a lambda, which is convertible to either
+      // std::function<F> or F*.
+      //
+      template <typename F1>
+      function_wrapper(F1,
+                       typename std::enable_if<
+                       !std::is_convertible<F1, F*>::value>::type* = 0);
+#endif
+
+      // Destructive copy construction and assignment (aka move). These
+      // should really only be called by containers when they need to
+      // reallocate the underlying buffer and move the elements.
+      //
+      function_wrapper (const function_wrapper<F>&);
+      function_wrapper&
+      operator= (const function_wrapper<F>&);
+
+      void swap (function_wrapper<F>&);
+
+      // Conversion to bool.
+      //
+    public:
+      typedef void (function_wrapper<F>::*bool_convertible) ();
+      void true_value () {}
+
+      operator bool_convertible () const;
+
+    public:
+      F* function;
+      void (*deleter) (const void*);
+      const void* std_function;
+    };
+  }
+}
+
+#include <odb/details/function-wrapper.ixx>
+#include <odb/details/function-wrapper.txx>
+
+#include <odb/post.hxx>
+
+#endif // ODB_DETAILS_FUNCTION_WRAPPER_HXX
diff --git a/odb/details/function-wrapper.ixx b/odb/details/function-wrapper.ixx
new file mode 100644
index 0000000..58ede04
--- /dev/null
+++ b/odb/details/function-wrapper.ixx
@@ -0,0 +1,47 @@
+// file      : odb/details/function-wrapper.ixx
+// copyright : Copyright (c) 2009-2014 Code Synthesis Tools CC
+// license   : GNU GPL v2; see accompanying LICENSE file
+
+namespace odb
+{
+  namespace details
+  {
+    template <typename F>
+    inline function_wrapper<F>::
+    ~function_wrapper ()
+    {
+      if (deleter != 0)
+        deleter (std_function);
+    }
+
+    template <typename F>
+    inline function_wrapper<F>::
+    function_wrapper (F* f)
+        : function (f), deleter (0), std_function (0)
+    {
+    }
+
+    template <typename F>
+    inline function_wrapper<F>::
+    function_wrapper (const function_wrapper<F>& x)
+        : function (0), deleter (0), std_function (0)
+    {
+      swap (const_cast<function_wrapper<F>&> (x));
+    }
+
+    template <typename F>
+    inline function_wrapper<F>& function_wrapper<F>::
+    operator= (const function_wrapper<F>& x)
+    {
+      swap (const_cast<function_wrapper<F>&> (x));
+      return *this;
+    }
+
+    template <typename F>
+    inline function_wrapper<F>::
+    operator bool_convertible () const
+    {
+      return function != 0 ? &function_wrapper<F>::true_value : 0;
+    }
+  }
+}
diff --git a/odb/details/function-wrapper.txx b/odb/details/function-wrapper.txx
new file mode 100644
index 0000000..70dcb0f
--- /dev/null
+++ b/odb/details/function-wrapper.txx
@@ -0,0 +1,87 @@
+// file      : odb/details/function-wrapper.txx
+// copyright : Copyright (c) 2009-2014 Code Synthesis Tools CC
+// license   : GNU GPL v2; see accompanying LICENSE file
+
+#include <utility> // std::swap, std::move
+
+namespace odb
+{
+  namespace details
+  {
+#ifdef ODB_CXX11
+    template <typename F>
+    struct caller_impl;
+
+#ifdef ODB_CXX11_VARIADIC_TEMPLATE
+    template <typename R, typename... A>
+    struct caller_impl<R (A...)>
+    {
+      static R
+      function (const void* f, A... a)
+      {
+        return (*static_cast<const std::function<R (A...)>*> (f)) (a...);
+      }
+    };
+#else
+    template <typename R, typename A1>
+    struct caller_impl<R (A1)>
+    {
+      static R
+      function (const void* f, A1 a1)
+      {
+        return (*static_cast<const std::function<R (A1)>*> (f)) (a1);
+      }
+    };
+
+    template <typename R, typename A1, typename A2>
+    struct caller_impl<R (A1, A2)>
+    {
+      static R
+      function (const void* f, A1 a1, A2 a2)
+      {
+        return (*static_cast<const std::function<R (A1, A2)>*> (f)) (a1, a2);
+      }
+    };
+#endif
+
+    template <typename F>
+    void
+    deleter_impl (const void* f)
+    {
+      delete static_cast<const std::function<F>*> (f);
+    }
+
+    template <typename F>
+    template <typename F1>
+    function_wrapper<F>::
+    function_wrapper (
+      F1 f,
+      typename std::enable_if<!std::is_convertible<F1, F*>::value>::type*)
+    {
+      std_function_type sf (std::move (f));
+
+      if (F* const* const f = sf.template target<F*> ())
+      {
+        function = *f;
+        deleter = 0;
+        std_function = 0;
+      }
+      else
+      {
+        function = reinterpret_cast<F*> (&caller_impl<F>::function);
+        deleter = &deleter_impl<F>;
+        std_function = new std_function_type (std::move (sf));
+      }
+    }
+#endif
+
+    template <typename F>
+    void function_wrapper<F>::
+    swap (function_wrapper<F>& x)
+    {
+      std::swap (function, x.function);
+      std::swap (deleter, x.deleter);
+      std::swap (std_function, x.std_function);
+    }
+  }
+}
diff --git a/odb/schema-catalog.cxx b/odb/schema-catalog.cxx
index d223647..f2df4e2 100644
--- a/odb/schema-catalog.cxx
+++ b/odb/schema-catalog.cxx
@@ -38,13 +38,15 @@ namespace odb
 
   struct data_function
   {
-    typedef schema_catalog::data_migration_function_type function_type;
+    typedef schema_catalog::data_migration_function_wrapper
+    function_wrapper_type;
 
     data_function () {}
-    data_function (database_id i, function_type m): id (i), migrate (m) {}
+    data_function (database_id i, function_wrapper_type m)
+        : id (i), migrate (m) {}
 
     database_id id;
-    function_type migrate;
+    function_wrapper_type migrate;
   };
   typedef vector<data_function> data_functions;
   typedef map<data_key, data_functions> data_map;
@@ -218,7 +220,15 @@ namespace odb
     {
       if (i->id == id_common || i->id == db.id ())
       {
-        i->migrate (db);
+        const data_migration_function_wrapper &m = i->migrate;
+
+        if (m.std_function == 0)
+          m.function (db);
+        else
+        {
+          typedef void (*caller) (const void*, database&);
+          reinterpret_cast<caller> (m.function) (m.std_function, db);
+        }
         r++;
       }
     }
@@ -229,7 +239,7 @@ namespace odb
   void schema_catalog::
   data_migration_function (database_id id,
                            schema_version v,
-                           data_migration_function_type f,
+                           data_migration_function_wrapper f,
                            const string& name)
   {
     // This function can be called from a static initializer in which
diff --git a/odb/schema-catalog.hxx b/odb/schema-catalog.hxx
index 7d675fe..510126a 100644
--- a/odb/schema-catalog.hxx
+++ b/odb/schema-catalog.hxx
@@ -13,7 +13,9 @@
 #include <cstddef> // std::size_t
 
 #ifdef ODB_CXX11
-#  include <functional> // std::function
+#  include <utility>     // std::move
+#  include <functional>  // std::function
+#  include <type_traits> // std::enable_if, std::is_convertible
 #endif
 
 #include <odb/forward.hxx> // schema_version, odb::core
@@ -74,11 +76,11 @@ namespace odb
                   schema_version = 0,
                   const std::string& name = "");
 
-#ifdef ODB_CXX11
-    typedef std::function<void (database&)> data_migration_function_type;
-#else
-    typedef void (*data_migration_function_type) (database&);
-#endif
+    typedef void data_migration_function_type (database&);
+    typedef data_migration_function_type* data_migration_function_ptr;
+
+    typedef details::function_wrapper<data_migration_function_type>
+    data_migration_function_wrapper;
 
     // The following three variants of the registration functions make
     // sure that the version is greater that the base model version.
@@ -87,38 +89,59 @@ namespace odb
     //
     // Data migration functions are called in the order of registration.
     //
+#ifndef ODB_CXX11
     template <schema_version v, schema_version base>
     static void
-    data_migration_function (data_migration_function_type f,
+    data_migration_function (data_migration_function_ptr f,
                              const std::string& name = "")
     {
       data_migration_function<v, base> (id_common, f, name);
     }
 
+#else
+    template <schema_version v, schema_version base, typename F>
+    static typename std::enable_if<
+      std::is_convertible<
+        F, std::function<data_migration_function_type>>::value, void>::type
+    data_migration_function (F f, const std::string& name = "")
+    {
+      data_migration_function<v, base> (id_common, std::move (f), name);
+    }
+#endif
+
     // Database-specific data migration.
     //
+#ifndef ODB_CXX11
     template <schema_version v, schema_version base>
     static void
     data_migration_function (database& db,
-                             data_migration_function_type f,
+                             data_migration_function_ptr f,
                              const std::string& name = "")
     {
       data_migration_function<v, base> (db.id (), f, name);
     }
+#else
+    template <schema_version v, schema_version base, typename F>
+    static typename std::enable_if<
+      std::is_convertible<
+        F, std::function<data_migration_function_type>>::value, void>::type
+    data_migration_function (database& db, F f, const std::string& name = "")
+    {
+      data_migration_function<v, base> (db.id (), std::move (f), name);
+    }
+#endif
 
+#ifndef ODB_CXX11
     template <schema_version v, schema_version base>
     static void
     data_migration_function (database_id id,
-                             data_migration_function_type f,
+                             data_migration_function_ptr f,
                              const std::string& name = "")
     {
       // If the data migration version is below the base model version
       // then it will never be called.
       //
-#ifdef ODB_CXX11
-      static_assert (v > base || base == 0,
-                     "data migration function is no longer necessary");
-#else
+
       // Poor man's static_assert.
       //
       typedef details::meta::static_assert_test<(v > base || base == 0)>
@@ -126,36 +149,109 @@ namespace odb
 
       char sa [sizeof (data_migration_function_is_no_longer_necessary)];
       ODB_POTENTIALLY_UNUSED (sa);
-#endif
 
       data_migration_function (id, v, f, name);
     }
+#else
+    template <schema_version v, schema_version base, typename F>
+    static typename std::enable_if<
+      std::is_convertible<
+        F, std::function<data_migration_function_type>>::value, void>::type
+    data_migration_function (database_id id, F f, const std::string& name = "")
+    {
+      // If the data migration version is below the base model version
+      // then it will never be called.
+      //
+      static_assert (v > base || base == 0,
+                     "data migration function is no longer necessary");
+
+      data_migration_function (id, v, std::move (f), name);
+    }
+#endif
 
     // The same as above but take the version as an argument and do
     // not check whether it is greater than the base model version.
     //
+#ifndef ODB_CXX11
     static void
     data_migration_function (schema_version v,
-                             data_migration_function_type f,
+                             data_migration_function_ptr f,
                              const std::string& name = "")
     {
       data_migration_function (id_common, v, f, name);
     }
+#else
+    template <typename F>
+    static typename std::enable_if<
+      std::is_convertible<
+        F, std::function<data_migration_function_type>>::value, void>::type
+    data_migration_function (schema_version v,
+                             F f,
+                             const std::string& name = "")
+    {
+      data_migration_function (id_common, v, std::move (f), name);
+    }
+#endif
 
+#ifndef ODB_CXX11
     static void
     data_migration_function (database& db,
                              schema_version v,
-                             data_migration_function_type f,
+                             data_migration_function_ptr f,
                              const std::string& name = "")
     {
       data_migration_function (db.id (), v, f, name);
     }
+#else
+    template <typename F>
+    static typename std::enable_if<
+      std::is_convertible<
+        F, std::function<data_migration_function_type>>::value, void>::type
+    data_migration_function (database& db,
+                             schema_version v,
+                             F f,
+                             const std::string& name = "")
+    {
+      data_migration_function (db.id (), v, std::move (f), name);
+    }
+#endif
+
+#ifndef ODB_CXX11
+    static void
+    data_migration_function (database_id i,
+                             schema_version v,
+                             data_migration_function_ptr f,
+                             const std::string& name = "")
+    {
+      data_migration_function (i,
+                               v,
+                               data_migration_function_wrapper (f),
+                               name);
+    }
+#else
+    template <typename F>
+    static typename std::enable_if<
+      std::is_convertible<
+        F, std::function<data_migration_function_type>>::value, void>::type
+    data_migration_function (database_id i,
+                             schema_version v,
+                             F f,
+                             const std::string& name = "")
+    {
+      data_migration_function (
+        i,
+        v,
+        data_migration_function_wrapper (std::move (f)),
+        name);
+    }
+#endif
 
+  private:
     static void
     data_migration_function (database_id,
                              schema_version,
-                             data_migration_function_type,
-                             const std::string& name = "");
+                             data_migration_function_wrapper,
+                             const std::string& name);
 
     // Combined schema and data migration.
     //
@@ -244,17 +340,45 @@ namespace odb
   {
     typedef schema_catalog::data_migration_function_type function_type;
 
-    data_migration_entry (function_type f, const std::string& name = "")
+#ifndef ODB_CXX11
+    data_migration_entry (function_type* f, const std::string& name = "")
     {
       schema_catalog::data_migration_function<v, base> (f, name);
     }
+#else
+    template <typename F>
+    data_migration_entry (F f,
+                          const std::string& name = "",
+                          typename std::enable_if<std::is_convertible<
+                            F, std::function<function_type>>::value>
+                          ::type* = 0)
+    {
+      schema_catalog::data_migration_function<v, base> (std::move (f), name);
+    }
+#endif
 
+#ifndef ODB_CXX11
     data_migration_entry (database_id id,
-                          function_type f,
+                          function_type *f,
                           const std::string& name = "")
     {
       schema_catalog::data_migration_function<v, base> (id, v, f, name);
     }
+#else
+    template <typename F>
+    data_migration_entry (database_id id,
+                          F f,
+                          const std::string& name = "",
+                          typename std::enable_if<std::is_convertible<
+                            F, std::function<function_type>>::value>
+                          ::type* = 0)
+    {
+      schema_catalog::data_migration_function<v, base> (id,
+                                                        v,
+                                                        std::move (f),
+                                                        name);
+    }
+#endif
   };
 
   namespace common
-- 
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