From 75b5a927c8293dfe1b4f7fd649afb14bd4e0fb94 Mon Sep 17 00:00:00 2001
From: Scott Giese <scttgs0@gmail.com>
Date: Tue, 5 Feb 2019 12:20:06 -0600
Subject: [PATCH] [boost::enable_if] Support Boost versions < 1.56

---
 simgear/nasal/cppbind/NasalHash.hxx    | 4 ++++
 simgear/props/props.hxx                | 6 +++++-
 simgear/structure/SGWeakReferenced.hxx | 4 ++++
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/simgear/nasal/cppbind/NasalHash.hxx b/simgear/nasal/cppbind/NasalHash.hxx
index 5019d08b..59281643 100644
--- a/simgear/nasal/cppbind/NasalHash.hxx
+++ b/simgear/nasal/cppbind/NasalHash.hxx
@@ -24,7 +24,11 @@
 
 #include <simgear/structure/map.hxx>
 #include <boost/iterator/iterator_facade.hpp>
+#if BOOST_VERSION >= 105600
 #include <boost/core/enable_if.hpp>
+#else
+#include <boost/utility/enable_if.hpp>
+#endif
 
 namespace nasal
 {
diff --git a/simgear/props/props.hxx b/simgear/props/props.hxx
index 68d3c03c..3afc8796 100644
--- a/simgear/props/props.hxx
+++ b/simgear/props/props.hxx
@@ -56,7 +56,11 @@ namespace boost {
 }
 #else
 # include <boost/type_traits/is_enum.hpp>
-# include <boost/core/enable_if.hpp>
+#if BOOST_VERSION >= 105600
+#include <boost/core/enable_if.hpp>
+#else
+#include <boost/utility/enable_if.hpp>
+#endif
 
 # include <simgear/debug/logstream.hxx>
 # include <simgear/math/SGMathFwd.hxx>
diff --git a/simgear/structure/SGWeakReferenced.hxx b/simgear/structure/SGWeakReferenced.hxx
index 27f647b4..24db41b8 100644
--- a/simgear/structure/SGWeakReferenced.hxx
+++ b/simgear/structure/SGWeakReferenced.hxx
@@ -22,7 +22,11 @@
 #include "SGSharedPtr.hxx"
 
 #include <boost/type_traits/is_base_of.hpp>
+#if BOOST_VERSION >= 105600
 #include <boost/core/enable_if.hpp>
+#else
+#include <boost/utility/enable_if.hpp>
+#endif
 
 #ifdef _MSC_VER
 # pragma warning(push)