Object-oriented Software in Ada 95

236 Polymorphism
The function about uses a linear search to find the selected room number. If the room number does not exist,
the returned string contains the text "Sorry room not known".
function About(The:in Building; No:in Positive) return String is
begin
for I in 1 .. The.Last loop
if Where(The.Description(I).all) = No then
return Describe(The.Description(I).all);
end if;
end loop;
return "Sorry room not known";
end About;
end Class_Building;
Note:
Chapter 17 explores more sophisticated container implementations.
The appending of .all to an access value causes the object described by the access value to be
delivered.
16.5.1 Putting it all together
The classes Room, Office and Building can be used to build a program to allow visitors to a building to find
out details about individual rooms. The program is split into two procedures. The first procedure declares and sets
up details about individual rooms in the building.
with Ada.Text_Io,Ada.Integer_Text_Io,Class_Room,Class_Room.Build,
Class_Office, Class_Office.Build, Class_Building;
use Ada.Text_Io,Ada.Integer_Text_Io,Class_Room,Class_Room.Build,
Class_Office, Class_Office.Build, Class_Building;
procedure Set_Up( Watts:in out Building ) is
begin
Add( Watts, Build_Office( 414, "4th Floor west wing", 2 ) );
Add( Watts, Build_Room ( 422, "4th Floor east wing" ) );
end Set_Up;
The second procedure interrogates the object watts to find details about individual rooms.
with Ada.Text_Io, Ada.Integer_Text_Io, Class_Building, Set_Up;
use Ada.Text_Io, Ada.Integer_Text_Io, Class_Building;
procedure Main is
Watts : Building;
--Watts Building
Room_No : Positive;
--Queried room
begin
Set_Up( Watts );
--Populate building
loop
begin
Put( "Inquiry about room: " ); --Ask
exit when End_Of_File;
Get( Room_No ); Skip_Line; --User response
Put( About( Watts, Room_No ) );
New_Line;
--Display answer
exception
when Data_Error =>
Put("Please retype the number"); --Ask again
New_Line; Skip_Line;
end;
end loop;
end Main;
Note:
The program does not release the storage for the descriptions of the individual rooms and offices.
© M A Smith - May not be reproduced without permission