allow or disallow overriding options

lib/ProgramOptions2/ProgramOptions.h

@@ -105,9 +105,15 @@ class ProgramOptions {
   ProcessingResult& processingResult() { return _processingResult; }
 
   // seal the options
-  // tryin to add an option or a section after sealing will throw an error
+  // trying to add an option or a section after sealing will throw an error
   void seal() { _sealed = true; }
 
+  // allow or disallow overriding already set options
+  bool allowOverride(bool value) {
+    checkIfSealed();
+    _overrideOptions = value;
+  }
+
   // set context for error reporting
   void setContext(std::string const& value) { _context = value; }
 
@@ -260,6 +266,11 @@ class ProgramOptions {
 
   // sets a value for an option
   bool setValue(std::string const& name, std::string const& value) {
+    if (!_overrideOptions && _processingResult.touched(name)) {
+      // option already set. don't override it
+      return true;
+    } 
+
     auto parts = Option::splitName(name);
     auto it = _sections.find(parts.first);
 
@@ -463,6 +474,8 @@ class ProgramOptions {
   ProcessingResult _processingResult;
   // whether or not the program options setup is still mutable
   bool _sealed;
+  // allow or disallow overriding already set options
+  bool _overrideOptions;
 };
 }
 }