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/details/function-wrapper.hxx | 83 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 83 insertions(+)
 create mode 100644 odb/details/function-wrapper.hxx

(limited to 'odb/details/function-wrapper.hxx')

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
-- 
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