A base class for unary operators. 
 
A base class for unary functions. 
 
Expression * clone() const 
It creates a new copy of this expression. 
 
This is an abstract class that models a query expression. 
 
UnaryOp & operator=(const UnaryOp &rhs)
 
UnaryFunction & operator=(const UnaryFunction &rhs)
 
UnaryOp(const std::string &name, Expression *arg)
Constructor. 
 
A base class for unary operators.