C++17 modernization: use std::optional for “periods” option of “plot_conditional_forecast”

Incidentally, in the JSON output, no longer assign a value to the “periods”
field if not passed by the user (previously the value -1 was output in the JSON
file).

src/ComputingTasks.cc

@@ -3266,10 +3266,10 @@ ConditionalForecastStatement::writeJsonOutput(ostream &output) const
   output << "}";
 }
 
-PlotConditionalForecastStatement::PlotConditionalForecastStatement(int periods_arg,
+PlotConditionalForecastStatement::PlotConditionalForecastStatement(optional<int> periods_arg,
                                                                    SymbolList symbol_list_arg,
                                                                    const SymbolTable &symbol_table_arg) :
-  periods{periods_arg},
+  periods{move(periods_arg)},
   symbol_list{move(symbol_list_arg)},
   symbol_table{symbol_table_arg}
 {
@@ -3294,17 +3294,18 @@ void
 PlotConditionalForecastStatement::writeOutput(ostream &output, const string &basename, bool minimal_workspace) const
 {
   symbol_list.writeOutput("var_list_", output);
-  if (periods == -1)
-    output << "plot_icforecast(var_list_,[],options_,oo_);" << endl;
+  if (periods)
+    output << "plot_icforecast(var_list_, " << *periods << ",options_,oo_);" << endl;
   else
-    output << "plot_icforecast(var_list_, " << periods << ",options_,oo_);" << endl;
+    output << "plot_icforecast(var_list_,[],options_,oo_);" << endl;
 }
 
 void
 PlotConditionalForecastStatement::writeJsonOutput(ostream &output) const
 {
-  output << R"({"statementName": "plot_conditional_forecast", )"
-         << R"("periods": )" << periods;
+  output << R"({"statementName": "plot_conditional_forecast")";
+  if (periods)
+    output << R"(, "periods": )" << *periods;
   if (!symbol_list.empty())
     {
       output << ", ";

src/ComputingTasks.hh

@@ -21,6 +21,7 @@
 #define _COMPUTINGTASKS_HH
 
 #include <ostream>
+#include <optional>
 
 #include "SymbolList.hh"
 #include "SymbolTable.hh"
@@ -848,12 +849,11 @@ public:
 class PlotConditionalForecastStatement : public Statement
 {
 private:
-  //! A value of -1 indicates that the user didn't specify a value
-  const int periods;
+  const optional<int> periods; // The user is allowed not to declare periods
   const SymbolList symbol_list;
   const SymbolTable &symbol_table;
 public:
-  PlotConditionalForecastStatement(int periods_arg, SymbolList symbol_list_arg,
+  PlotConditionalForecastStatement(optional<int> periods_arg, SymbolList symbol_list_arg,
                                    const SymbolTable &symbol_table_arg);
   void checkPass(ModFileStructure &mod_file_struct, WarningConsolidation &warnings) override;
   void writeOutput(ostream &output, const string &basename, bool minimal_workspace) const override;

src/DynareBison.yy

@@ -3213,7 +3213,7 @@ conditional_forecast_option : o_periods
                             ;
 
 plot_conditional_forecast : PLOT_CONDITIONAL_FORECAST symbol_list ';'
-                            { driver.plot_conditional_forecast("", $2); }
+                            { driver.plot_conditional_forecast(nullopt, $2); }
                           | PLOT_CONDITIONAL_FORECAST '(' PERIODS EQUAL INT_NUMBER ')' symbol_list ';'
                             { driver.plot_conditional_forecast($5, $7); }
                           ;

src/ParsingDriver.cc

@@ -2498,10 +2498,12 @@ ParsingDriver::conditional_forecast()
 }
 
 void
-ParsingDriver::plot_conditional_forecast(const string &periods, vector<string> symbol_list)
+ParsingDriver::plot_conditional_forecast(const optional<string> &periods, vector<string> symbol_list)
 {
-  int nperiods = periods.empty() ? -1 : stoi(periods);
-  mod_file->addStatement(make_unique<PlotConditionalForecastStatement>(nperiods, move(symbol_list),
+  optional<int> iperiods;
+  if (periods)
+    iperiods = stoi(*periods);
+  mod_file->addStatement(make_unique<PlotConditionalForecastStatement>(move(iperiods), move(symbol_list),
                                                                        mod_file->symbol_table));
 }
 

src/ParsingDriver.hh

@@ -726,7 +726,7 @@ public:
   //! Conditional forecast paths block
   void conditional_forecast_paths();
   //! Plot conditional forecast statement
-  void plot_conditional_forecast(const string &periods, vector<string> symbol_list);
+  void plot_conditional_forecast(const optional<string> &periods, vector<string> symbol_list);
   //! Smoother on calibrated models
   void calib_smoother(vector<string> symbol_list);
   //! Extended path