Add operator for concatenating strings and string_views

src/libutil/util.hh

@@ -700,4 +700,19 @@ template<class... Ts> overloaded(Ts...) -> overloaded<Ts...>;
 std::string showBytes(uint64_t bytes);
 
 
+/* Provide an addition operator between strings and string_views
+   inexplicably omitted from the standard library. */
+inline std::string operator + (const std::string & s1, std::string_view s2)
+{
+    auto s = s1;
+    s.append(s2);
+    return s;
+}
+
+inline std::string operator + (std::string && s, std::string_view s2)
+{
+    s.append(s2);
+    return s;
+}
+
 }