Restarted the production of the app

libs/CLI11/examples/callback_passthrough.cpp

@@ -0,0 +1,28 @@
+// Copyright (c) 2017-2022, University of Cincinnati, developed by Henry Schreiner
+// under NSF AWARD 1414736 and by the respective contributors.
+// All rights reserved.
+//
+// SPDX-License-Identifier: BSD-3-Clause
+
+#include <CLI/CLI.hpp>
+#include <iostream>
+#include <string>
+
+int main(int argc, char **argv) {
+
+    CLI::App app("callback_passthrough");
+    app.allow_extras();
+    std::string argName;
+    std::string val;
+    app.add_option("--argname", argName, "the name of the custom command line argument");
+    app.callback([&app, &val, &argName]() {
+        if(!argName.empty()) {
+            CLI::App subApp;
+            subApp.add_option("--" + argName, val, "custom argument option");
+            subApp.parse(app.remaining_for_passthrough());
+        }
+    });
+
+    CLI11_PARSE(app, argc, argv);
+    std::cout << "the value is now " << val << '\n';
+}