Object-oriented Software in Ada 95

256 Containers
When comparing two lists, the physical storage of the list needs to be compared, rather than the access values
which point to the storage for the list. Remember, two lists may contain equal contents yet be represented by
different physical lists.
function "=" ( F:in List; S:in List ) return Boolean is
F_Node : P_Node := F.First_Node; --First list
S_Node : P_Node := S.First_Node; --Second list
begin
while F_Node /= null and S_Node /= null loop
if F_Node.Item /= S_Node.Item then
return False; --Different items
end if;
F_Node := F_Node.Next; S_Node := S_Node.Next;
end loop;
return F_Node = S_Node; --Both NULL if equal
end "=";
Note: When = is overloaded, /= is also overloaded with the definition of not =.
This is true for = which returns a Boolean value.
17.3.1 The list iterator
The specification for the iterator, which is implemented as a child package of the package Class_List, is:
generic
package Class_List.Iterator is
type List_Iter is limited private;
procedure First( The:in out List_Iter; L:in out List );
procedure Last( The:in out List_Iter; L:in out List );
function Deliver( The:in List_Iter) return T;
procedure Insert( The:in out List_Iter; Data:in T );
procedure Delete( The:in out List_Iter );
function Is_End( The:in List_Iter ) return Boolean;
procedure Next( The:in out List_Iter );
procedure Prev( The:in out List_Iter );
private
type P_P_Node is access all P_Node;
type List_Iter is record
Cur_List_First: P_P_Node := null; --First in chain
Cur_List_Last : P_P_Node := null; --Last in chain
Cur_Node : P_Node := null; --Current item
end record;
end Class_List.Iterator;
Note:
The child package Class_List.Iterator must be generic as its parent is generic.
© M A Smith - May not be reproduced without permission