Virtuality with a variadic interface.

virtual_variadic.cpp

#include <string>
#include <sstream>
#include <iostream>
#include <memory>

struct Serializer {
  virtual ~Serializer() {}

  virtual void StartRecord() = 0;
  virtual void EndRecord() = 0;
  virtual std::string GetRecord() const = 0;

  virtual void Push(int value) = 0;
  virtual void Push(double value) = 0;
  virtual void Push(std::string const& value) = 0;
  // etc avec tous les types possibles
};

class SerializerCSV : public Serializer {
  std::ostringstream record_stream_;
  std::string result_;
  bool has_data_ = false;

  void PushSep() {
    if (has_data_) record_stream_ << ';';
    has_data_ = true;
  }

 public:
  void StartRecord() override {
    result_ = "";
    record_stream_.str("");
    has_data_ = false;
  }

  void EndRecord() override { result_ = record_stream_.str(); }
  std::string GetRecord() const override { return result_; }
  void Push(int value) override { PushSep(); record_stream_ << value; } 
  void Push(double value) override { PushSep(); record_stream_ << value; }
  void Push(std::string const& value) override { PushSep(); record_stream_ << value; }
};

class SerializerJSON : public Serializer {
  std::ostringstream record_stream_;
  std::string result_;
  bool has_data_ = false;

  void PushSep() {
    if (has_data_) record_stream_ << ',';
    has_data_ = true;
  }

 public:
  void StartRecord() override {
    result_ = "";
    record_stream_.str("");
    record_stream_ << "[";
    has_data_ = false;
  }

  void EndRecord() override { 
    record_stream_ << ']';
    result_ = record_stream_.str(); 
  }
  std::string GetRecord() const override { return result_; }
  void Push(int value) override { PushSep(); record_stream_ << value; } 
  void Push(double value) override { PushSep(); record_stream_ << value; }
  void Push(std::string const& value) override { PushSep(); record_stream_ << '"' << value << '"'; }
};

class NetworkSerializer {
  std::unique_ptr<Serializer> serializer_impl_;

  void Push() {}
  template <typename Arg, typename ... Args> void Push(Arg value, Args ... values) {
    serializer_impl_->Push(value);
    Push(values ...);
  }

 public:
  void SetSerializerImpl(std::unique_ptr<Serializer>&& serializer) { serializer_impl_ = std::move(serializer); }
  void SetSerializerImpl(Serializer* serializer) { SetSerializerImpl(std::unique_ptr<Serializer>(serializer)); }

  template <typename ... Args> std::string Serialize(Args ... values) {
    serializer_impl_->StartRecord();
    Push(values...);
    serializer_impl_->EndRecord();
    return serializer_impl_->GetRecord();
  }
};

int main() {
  NetworkSerializer ns_dumper;
  
  ns_dumper.SetSerializerImpl(new SerializerCSV);
  std::cout << ns_dumper.Serialize(1, 2.3,"Roger",4) << "\n";

  ns_dumper.SetSerializerImpl(new SerializerJSON);
  std::cout << ns_dumper.Serialize(2.3, 1,"Roger",4,"Marcel") << "\n";

  return 0;
}