generics.cpp

class ASTNode {
public:
  template <class T> virtual T accept(Visitor<T> *visitor);
};

template <class T> class Visitor {
public:
  virtual T visit(CallNode *node) = 0;
  virtual T visit(BinExprNode *node) = 0;
};

class Optimizer : public Visitor<ASTNode *> {
public:
  ASTNode *visit(BinExprNode *node) {
    ASTNode *optimizedL = <ASTNode *>node->left()->accept(this);
    ASTNode *optimizedR = <ASTNode *>node->right()->accept(this);
    return new BinExprNode(optimizedL, node->op(), optimizedR);
  }
};