Object-oriented Software in Ada 95

Dynamic memory allocation 221
A benifit of the approach taken above is that a client of the class only needs to relink with any new
implementation code even though the implementor of the class has changed the data in the object.
The implementation of the revised class Account is as follows:
with Unchecked_Deallocation;
package body Class_Account is
pragma Controlled( P_Actual_Account ); -- We do deallocation
type Actual_Account is record --Hidden declaration
Balance_Of : Money := 0.00; --Amount in account
end record;
The code for Initialize allocates the storage for the object automatically when an instance of the class is
created. The body of finalize releases the storage when the object goes out of scope.
procedure Dispose is
new Unchecked_Deallocation(Actual_Account, P_Actual_Account);
procedure Initialize( The:in out Account ) is
begin
The.Acc := new Actual_Account; --Allocate storage
end Initialize;
procedure Finalize ( The:in out Account ) is
begin
if The.Acc /= null then --Release storage
Dispose(The.Acc); The.Acc:= null; --Note can be called
end if;
-- more than once
end Finalize;
The code for Deposit, Withdraw and Balance are similar to the previous implementation of Account.
procedure Deposit ( The:in out Account; Amount:in Pmoney ) is
begin
The.Acc.Balance_Of := The.Acc.Balance_Of + Amount;
end Deposit;
procedure Withdraw( The:in out Account; Amount:in Pmoney;
Get:out Pmoney ) is
begin
if The.Acc.Balance_Of >= Amount then
The.Acc.Balance_Of := The.Acc.Balance_Of - Amount;
Get := Amount;
else
Get := 0.00;
end if;
end Withdraw;
function Balance( The:in Account ) return Money is
begin
return The.Acc.Balance_Of;
end Balance;
end Class_Account;
Note:
The automatic de-referencing of The.
© M A Smith - May not be reproduced without permission