Object-oriented Software in Ada 95

Containers 271
17.7.1 Putting it all together
The program below illustrates the use of a set to record the ingredients in a sandwich.
package Pack_Types is
type Filling is ( Cheese, Onion, Ham, Tomato );
end Pack_Types;
with Ada.Text_Io, Pack_Types;
use Ada.Text_Io, Pack_Types;
procedure Put_Filling( C:in Filling ) is
begin
Put( Filling'Image( C ) );
end Put_Filling;
with Pack_Types, Class_Set, Put_Filling;
use Pack_Types;
pragma Elaborate_All( Class_Set );
package Class_Set_Sandwich is
new Class_Set( T => Pack_Types.Filling, Put => Put_Filling );
with Pack_Types, Ada.Text_Io, Ada.Integer_Text_Io, Class_Set_Sandwich;
use Pack_Types, Ada.Text_Io, Ada.Integer_Text_Io, Class_Set_Sandwich;
procedure Main is
Sandwich : Class_Set_Sandwich.Set;
begin
Sandwich := Sandwich + Set_Const(Cheese);
Sandwich := Sandwich + Set_Const(Onion) ;
Put("Contents of sandwich are : ");
Put( Sandwich ); New_Line;
Put("Number of ingredients is : ");
Put( Members(Sandwich) ); New_Line;
null;
end Main;
Note:
The instantiation of the class Class_Set_Sandwich uses the default definitions of > and < taken
from the environment.
An instantiation of a class which is inherited from Controlled must be at the library level.
which when run, will produce the following results:
Contents of sandwich are : (CHEESE,ONION)
Number of ingredients is : 2
17.8 Self-assessment
• What is the purpose of an iterator?
• When inheriting from Controlled, the user can provide the following procedures:
Finalize, Initialize, and Adjust.
What is the purpose of these procedures?
• If A and B are controlled objects, what happens when the assignment:
A := B;
is made?
• What is the difference between a deep and a shallow copy?
© M A Smith - May not be reproduced without permission