Object-oriented Software in Ada 95

258 Containers
The code for Insert is complex due to the necessity of handling insertion at different places in the linked
list. In particular, the list’s access values to the physical storage of the list will need to be updated. Remember, the
iterator only knows about the current position in the list.
In the implementation of Insert there are four distinct cases to handle when a data item is inserted. This is
summarized in the table below:
Position
On an empty list
Beyond the last item in the list
Before the first item
In the middle of the list
Commentary
Will need to update the list’s access values
Cur_List_First and Cur_List_Last as
well as update the current position Cur_Node in
the iterator.
Will need to update the list’s access value
Cur_List_Last as well as update the current
position Cur_Node in the iterator.
Will need to update the list’s access value
Cur_List_First.
No updating required to the list’s access values
nor the current position of the iterator.
The implementation of the insert procedure is as follows:
procedure Insert( The:in out List_Iter; Data:in T ) is
Tmp : P_Node;
Cur : P_Node := The.Cur_Node; --Current element
First : P_P_Node := The.Cur_List_First;
Last : P_P_Node := The.Cur_List_Last;
begin
if Cur = null then --Empty or last item
if First.all = null then -- Empty list
Tmp := new Node'( null, Data, null );
First.all := Tmp;
Last.all := Tmp;
The.Cur_Node := Tmp;
else
-- Last
Tmp := new Node'( Last.all, Data, null );
Last.all.Next := Tmp;
Last.all := Tmp;
The.Cur_Node := Tmp;
end if;
else
Tmp := new Node'( Cur.Prev, Data, Cur );
if Cur.Prev = null then --First item
First.all := Tmp;
else
Cur.Prev.Next := Tmp;
end if;
Cur.Prev := Tmp;
end if;
end Insert;
© M A Smith - May not be reproduced without permission