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diff --git a/common/safe-bool.h b/common/safe-bool.h
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+/**
+ * Boost Software License - Version 1.0 - August 17th, 2003
+ *
+ * Permission is hereby granted, free of charge, to any person or organization
+ * obtaining a copy of the software and accompanying documentation covered by
+ * this license (the "Software") to use, reproduce, display, distribute,
+ * execute, and transmit the Software, and to prepare derivative works of the
+ * Software, and to permit third-parties to whom the Software is furnished to
+ * do so, all subject to the following:
+ *
+ * The copyright notices in the Software and this entire statement, including
+ * the above license grant, this restriction and the following disclaimer,
+ * must be included in all copies of the Software, in whole or in part, and
+ * all derivative works of the Software, unless such copies or derivative
+ * works are solely in the form of machine-executable object code generated by
+ * a source language processor.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
+ * SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
+ * FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#ifndef COMMON_SAFE_BOOL_H
+#define COMMON_SAFE_BOOL_H
+
+namespace Common {
+	namespace impl {
+		template <typename T>
+		struct no_base {};
+
+		template <typename T>
+		struct safe_bool_impl {
+			typedef T *TP; // workaround to make parsing easier
+			TP stub;
+			typedef TP safe_bool_impl::*type;
+		};
+	}
+
+	/**
+	 * Prevents `operator bool` from implicitly converting to other types.
+	 */
+	template <typename DerivedT, typename BaseT = impl::no_base<DerivedT> >
+	struct SafeBool : BaseT {
+	private:
+		typedef impl::safe_bool_impl<DerivedT> impl_t;
+		typedef typename impl_t::type bool_type;
+
+	public:
+		operator bool_type() const {
+			return static_cast<const DerivedT *>(this)->operator_bool() ?
+			&impl_t::stub : 0;
+		}
+
+		operator bool_type() {
+			return static_cast<DerivedT *>(this)->operator_bool() ?
+			&impl_t::stub : 0;
+		}
+	};
+} // End of namespace Common
+
+#endif