I am writing a Gibbs sampler using Rcpp. I’m sampling many parameters in various structure: scalar, vector, matrix, so I defined a class “Model” to save all objects at each state. The class contains a member function to initialize, and a member function to update the current state according to data and the previous state.

However, when I run the following trunk, the members cpre, z, nu1mu, nu2mu, nu1sigma, nu2sigma were coupled. For example, these members of M0 was mistakenly updated when I call M1.update() and M2.update().

//[[Rcpp::export]]
int test1( int x,IntegerVector Data_i,IntegerVector Data_k,NumericVector Data_Y){
  Model M0;
  M0.initialize(x);
  
  Rcout<<"----------------Initialize-------------------"<<endl;
  M0.print();

  
  Model M1=M0;
  M1.update(Data_i,Data_k,Data_Y);

  
  Rcout<<"----------------Initialize after update-------------------"<<endl;
  M0.print();
  
   Model M2=M1;
   M2.update(Data_i,Data_k,Data_Y);
   
   Rcout<<"----------------Initialize after 2 update-------------------"<<endl;
   M0.print();
   
  return 0;
}

I have prevented coupling by redefining the “=” where each member was copied using clone() .

class Model{
public:
  int s;                    
  NumericMatrix cpre;              //??
  double mu;                
  NumericVector alpha;
  NumericVector rho;
  int nu1q;                 
  int nu2q;
  NumericVector nu1w;       
  NumericVector nu2w;
  IntegerVector nu1z;       //??
  IntegerVector nu2z;       //??
  List nu1Omega;            
  List nu2Omega;
  IntegerVector nu1m;       
  IntegerVector nu2m;
  double nu1tau;            
  double nu2tau;
  NumericVector nu1mu;      //??
  NumericVector nu2mu;       //??
  NumericVector nu1sigma;   //??
  NumericVector nu2sigma;       //??
  NumericMatrix nu;         
  

  
  void initialize(int nbmk);
  void update( const IntegerVector & Data_i, const IntegerVector& Data_k, const NumericVector& Data_Y);

  void print();
  
  
  Model &operator=(const Model& Mprev){
    if (this!=&Mprev){
      //copy Mprev
      this->s = (Mprev.s);
      this->cpre = clone(Mprev.cpre);
      this->mu = (Mprev.mu);
      this->alpha = clone(Mprev.alpha);
      this->rho = clone(Mprev.rho);
      this->nu1q = (Mprev.nu1q);
      this->nu2q = (Mprev.nu2q);
      this->nu1w = clone(Mprev.nu1w);
      this->nu2w = clone(Mprev.nu2w);
      this->nu1z = clone(Mprev.nu1z);
      this->nu2z = clone(Mprev.nu2z);
      this->nu1Omega = clone(Mprev.nu1Omega);
      this->nu2Omega = clone(Mprev.nu2Omega);
      this->nu1m = clone(Mprev.nu1m);
      this->nu2m = clone(Mprev.nu2m);
      this->nu1tau = (Mprev.nu1tau);
      this->nu2tau = (Mprev.nu2tau);
      this->nu1mu = clone(Mprev.nu1mu);
      this->nu2mu = clone(Mprev.nu2mu);
      this->nu1sigma = clone(Mprev.nu1sigma);
      this->nu2sigma = clone(Mprev.nu2sigma);
      this->nu = clone(Mprev.nu);
    }
    return*this;
  }
  
  
  
};

I dont understand how this could happen to these members. Do you have any ideas about how to prevent that?