Object-oriented Software in Ada 95

Inheritance 157
Note: The methods of the class Named_Account will be all the methods of an Account plus all the
methods of Name_Address plus any methods of Named_Account itself.
Unfortunately multiple inheritance is not directly supported in Ada 95. However, an easy work around is to
define the class Named_Account whose instance attributes are instances of the classes Account and
Name_Address. The public methods of the class Named_Account have the same specification as the
combined methods of Account and Named_Account except that the type of object operated on is an instance
of the class Named_Account.
The specification for the class Named_Account is shown below:
with Class_Account, Class_Name_Address;
use Class_Account, Class_Name_Address;
package Class_Named_Account is
type Named_Account is tagged private;
subtype Pmoney is Class_Account.Pmoney;
subtype Money is Class_Account.Money;
procedure Set( The:out Named_Account; Str:in String );
function Deliver_Line( The:in Named_Account;
Line:in Positive ) return String;
function Lines( The:in Named_Account ) return Positive;
procedure Deposit( The:in out Named_Account; Amount:in Pmoney );
procedure Withdraw( The:in out Named_Account; Amount:in Pmoney;
Get:out Pmoney );
function Balance( The:in Named_Account ) return Pmoney;
private
type Named_Account is tagged record
Acc : Account; --An account object
Naa : Name_Address; --A Name and address object
end record;
end Class_Named_Account;
Note:
To allow a client of the class Named_Account to directly use the subtype Money in the class
Account the declaration :
subtype Money is Class_Account.Money;
has been added to the class.
The implementation of the class Named_Account is split into three distinct parts:
• The implementation of the methods in Name_Address.
• The implementation of the methods in Account.
• The implementation of the methods of Named_Account itself.
The implementation of the methods in Named_Account which are inherited from Name_Address are as
follows:
© M A Smith - May not be reproduced without permission