operators: add simple ue2::totally_ordered class

src/util/operators.h

@@ -0,0 +1,60 @@
+/*
+ * Copyright (c) 2017, Intel Corporation
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *  * Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *  * Neither the name of Intel Corporation nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/**
+ * \brief Ordered operators: provides all the other compare operators for types
+ * that provide equal and less-than.
+ *
+ * This is similar to Boost's totally_ordered class, but much simpler and
+ * without injecting the boost namespace into ADL lookup.
+ */
+
+#ifndef UTIL_OPERATORS_H
+#define UTIL_OPERATORS_H
+
+namespace ue2 {
+
+/**
+ * \brief Ordered operators: provides all the other compare operators for types
+ * that provide equal and less-than.
+ *
+ * Simply inherit from this class with your class name as its template
+ * parameter.
+ */
+template<typename T>
+class totally_ordered {
+public:
+    friend bool operator!=(const T &a, const T &b) { return !(a == b); }
+    friend bool operator<=(const T &a, const T &b) { return !(b < a); }
+    friend bool operator>(const T &a, const T &b) { return b < a; }
+    friend bool operator>=(const T &a, const T &b) { return !(a < b); }
+};
+
+} // namespace
+
+#endif // UTIL_OPERATORS_H