code: func Field(pointerToAField interface{}, rigthOperand ...Expression) (exp Expression) {
  	if len(rigthOperand) == 0 {
  		return &FieldExpression{pointerToAField, nil}
  	}
  	return &FieldExpression{pointerToAField, rigthOperand[0]}
  }
docs: // Field is a helper function to address field of a structure.
  //
  // Example usage:
  //   Where(Field(&UsersTable.LastName, UsersTable, EQ('Bond'))
  //   // generates, for example, "WHERE last_name='Bond'"