Object-oriented Software in Ada 95

Inheritance 161
10.8.1 Implementation
The procedure Initialize is called whenever an instance of Account_At is elaborated. This procedure
checks if this is the first elaboration, determined by the reference count The_Active. If it is the first concurrent
elaboration then the audit trail file log.txt is opened in append mode and associated with the file descriptor
The_Audit_Trail.
with Ada.Text_Io, Ada.Integer_Text_Io, Ada.Float_Text_Io;
use Ada.Text_Io, Ada.Integer_Text_Io, Ada.Float_Text_Io;
package body Class_Account_At is
procedure Initialize( The:in out Account_At ) is
begin
The_Active := The_Active + 1; --Another object
if The_Active = 1 then -- first time for class
Open( File=>The_Audit_Trail,
Mode=>Append_File, Name=>"log.txt" );
end if;
end Initialize;
The procedure Finalize is called when the elaborated storage for an instance of Account_At goes out of
scope. The reference count of the number of active instantiations of Account_At is checked and when the last
concurrent instance goes out of scope the file descriptor The_Audit_Trail is closed.
procedure Finalize( The:in out Account_At ) is
begin
if The_Active = 1 then Close( The_Audit_Trail ); end if;
The_Active:=The_Active-1;
end Finalize;
The rest of the implementation follows very closely the previous implementation of the class Account with the
additional functionality of writing the audit trail record for each transaction performed.
procedure Deposit( The:in out Account_At; Amount:in Pmoney ) is
begin
The.Balance_Of := The.Balance_Of + Amount;
Audit_Trail( The, " Deposit : Amount = ", Amount );
end Deposit;
procedure Withdraw( The:in out Account_At;
Amount:in Pmoney; Get:out Pmoney ) is
begin
if The.Balance_Of >= Amount then
The.Balance_Of := The.Balance_Of - Amount;
Get := Amount;
else
Get := 0.00;
end if;
Audit_Trail( The, " Withdraw : Amount = ", Get );
end Withdraw;
function Balance( The:in Account_At ) return Money is
begin
Audit_Trail( The, " Balance : Balance = ", The.Balance_Of );
return The.Balance_Of;
end Balance;
end Class_Account_At;
© M A Smith - May not be reproduced without permission