From 7f9a0ba5741a4cd49118d5c75014f25996005927 Mon Sep 17 00:00:00 2001
From: Joe Herdman <joe@herdman.ca>
Date: Fri, 6 Sep 2019 01:34:50 -0400
Subject: [PATCH] Allow object_pool::construct() to use variadic template, if
 available.

---
 include/boost/pool/object_pool.hpp | 12 ++++++
 test/test_pool_alloc.cpp           | 66 ++++++++++++++++++++++++++++++
 2 files changed, 78 insertions(+)

diff --git a/include/boost/pool/object_pool.hpp b/include/boost/pool/object_pool.hpp
index 092f0178..cbaf5699 100644
--- a/include/boost/pool/object_pool.hpp
+++ b/include/boost/pool/object_pool.hpp
@@ -175,6 +175,18 @@ class object_pool: protected pool<UserAllocator>
        //! detail/pool_construct.bat and detail/pool_construct.sh are also provided to call m4, defining NumberOfArguments 
        //! to be their command-line parameter. See these files for more details.
     }
+#elif defined(BOOST_HAS_VARIADIC_TMPL) && defined(BOOST_HAS_RVALUE_REFS)
+    // When available, use variadic templates to avoid the older '.ipp'/'.m4' implementation
+    template <typename... Args>
+    element_type * construct(Args&&... args)
+    {
+        element_type* const ret = (malloc)();
+        if (ret == 0)
+            return ret;
+        try { new (ret) element_type(std::forward<Args>(args)...); }
+        catch (...) { (free)(ret); throw; }
+        return ret;
+    }
 #else
 // Include automatically-generated file for family of template construct() functions.
 // Copy .inc renamed .ipp to conform to Doxygen include filename expectations, PAB 12 Jan 11.
diff --git a/test/test_pool_alloc.cpp b/test/test_pool_alloc.cpp
index b0b50eab..d504c295 100644
--- a/test/test_pool_alloc.cpp
+++ b/test/test_pool_alloc.cpp
@@ -66,6 +66,20 @@ struct tester
         mem.check_in(this);
     }
 
+    tester(int a0, int a1)
+    {
+        set_values(a0, a1, -1, -1);
+
+        mem.check_in(this);
+    }
+
+    tester(int a0, const int& a1, int a2, const int a3)
+    {
+        set_values(a0, a1, a2, a3);
+
+        mem.check_in(this);
+    }
+
     tester(const tester &)
     {
         mem.check_in(this);
@@ -75,6 +89,32 @@ struct tester
     {
         mem.check_out(this);
     }
+
+    int stored_a0;
+    int stored_a1;
+    int stored_a2;
+    int stored_a3;
+
+    void set_values(int a0, int a1, int a2, int a3)
+    {
+        stored_a0 = a0;
+        stored_a1 = a1;
+        stored_a2 = a2;
+        stored_a3 = a3;
+    }
+
+    void check_values(int a0, int a1)
+    {
+        check_values(a0, a1, -1, -1);
+    }
+
+    void check_values(int a0, int a1, int a2, int a3)
+    {
+        BOOST_TEST( a0 == stored_a0 );
+        BOOST_TEST( a1 == stored_a1 );
+        BOOST_TEST( a2 == stored_a2 );
+        BOOST_TEST( a3 == stored_a3 );
+    }
 };
 
 // This is a wrapper around a UserAllocator. It just registers alloc/dealloc
@@ -163,6 +203,32 @@ void test()
             catch(const std::logic_error &) {}
         }
     }
+
+    {
+        // Test the 'pool.construct' with 2 ctor parameters
+        boost::object_pool<tester> pool;
+        for(int i=0; i < 5; ++i)
+        {
+            tester * newItem = pool.construct(i, 2*i);
+            newItem->check_values(i, 2*i);
+        }
+    }
+
+#if defined(BOOST_HAS_VARIADIC_TMPL) && defined(BOOST_HAS_RVALUE_REFS)
+    {
+        // Test the 'pool.construct' with 4 ctor parameters
+        //   Without variadic-templates, this functionality requires
+        //   that the end-user has run the 'detail/pool_construct.m4'
+        //   functionality to generate a larger set of 'construct()'
+        //   overloads. [see docs for object_pool::construct()]
+        boost::object_pool<tester> pool;
+        for(int i=0; i < 5; ++i)
+        {
+            tester * newItem = pool.construct(i, 2*i, 3*i, 5*i);
+            newItem->check_values(i, 2*i, 3*i, 5*i);
+        }
+    }
+#endif
 }
 
 void test_alloc()