It models the comparison operator - syntatic-suggar. 
 
BinaryOp & operator=(const BinaryOp &rhs)
 
EqualTo & operator=(const EqualTo &rhs)
 
TE_DEFINE_VISITABLE EqualTo(Expression *arg1, Expression *arg2)
Constructor. 
 
A base class for binary operations. 
 
This is an abstract class that models a query expression. 
 
It models the comparison operator. 
 
Expression * clone() const 
It creates a new copy of this expression.