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diff --git a/boost/contract/detail/static_local_var.hpp b/boost/contract/detail/static_local_var.hpp
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+++ b/boost/contract/detail/static_local_var.hpp
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+
+#ifndef BOOST_CONTRACT_DETAIL_STATIC_LOCAL_VAR_HPP_
+#define BOOST_CONTRACT_DETAIL_STATIC_LOCAL_VAR_HPP_
+
+// Copyright (C) 2008-2018 Lorenzo Caminiti
+// Distributed under the Boost Software License, Version 1.0 (see accompanying
+// file LICENSE_1_0.txt or a copy at http://www.boost.org/LICENSE_1_0.txt).
+// See: http://www.boost.org/doc/libs/release/libs/contract/doc/html/index.html
+
+namespace boost { namespace contract { namespace detail {
+
+// This is used to hold the state of this library (already checking assertions,
+// failure handers, mutexes, etc.). Local static variables are used instead of
+// global or class-level static variables to avoid ODR errors when this library
+// is used as header-only.
+
+// Use T's default constructor to init the local var.
+template<typename Tag, typename T>
+struct static_local_var {
+    static T& ref() {
+        static T data;
+        return data;
+    }
+};
+
+// Use `init` param to init local var (Init same as or convertible to T).
+// NOTE: Template specializations could be used to program both this and the
+// template above together but some pre-C++11 compilers give errors (e.g., Clang
+// without -std=c++11), plus the `_init` postfix is more readable at call site.
+template<typename Tag, typename T, typename Init, Init init>
+struct static_local_var_init {
+    static T& ref() {
+        static T data = init;
+        return data;
+    }
+};
+
+} } } // namespace
+       
+#endif // #include guard
+