Object-oriented Software in Ada 95

Containers 251
This mirrors closely the mechanism used to access sequentially the elements of an array in Ada.
The list is implemented as a generic class list and its generic child Iterator. The two classes allow the
elaboration of:
• The object numbers which is the list of natural numbers.
• The object num_it, an iterator which is used to step through the objects held in the list.
17.1.1 List vs. array
Criteria List Array
The number of items held can be increased √
r
at run-time.
Deletion of an item leaves no gap when the √
r
items are iterated through.
Random access is very efficient. r √
Note:
Ada array’s bounds are fixed once the declaration is elaborated.
17.2 Methods implemented in a list
The methods that are implemented in an instance of the class list are as follows:
Method Responsibility
Initialize Initialize the container.
Finalize Finish using the container object.
Adjust Used to facilitate a deep copy.
= Comparison of a list for equality.
Note: A full explanation of adjust can be found in Section 17.3.
Whilst the methods that are implemented in an instance of the class List_Iter are:
Method Responsibility
Initialize Initialize the iterator.
Finalize Finish using the iterator object.
Deliver Deliver the object held at the position indicated by the iterator.
First Set the current position of the iterator to the first object in the
list.
Last
Set the current position of the iterator to the last object in the list.
Insert Insert into the list an object before the current position of the
iterator.
Delete Remove and dispose of the object in the list which is specified
by the current position of the iterator.
Is_end Deliver true if the iteration on the container has reached the end.
Next
Prev
Move to the next item in the container and make that the current
position.
Move to the previous item in the container and make that the
current position.
17.2.1 Example of use
The following program illustrates the use of a list. In this program natural numbers are read and inserted in
ascending order into a list. The contents of the list are then printed.
© M A Smith - May not be reproduced without permission