Object-oriented Software in Ada 95

288 Persistence
The procedure Find uses a recursive descent of the tree to find the selected index. If the index is not found,
then the exception Not_There is raised.
function Find( The:in Subtree; I:in Index) return Subtree is
begin
if The = null then raise Not_There; end if;
if I = The.Rec.S_Index then
return The;
--Found
else
if I > The.Rec.S_Index
then return Find( The.Right, I ); --Try RHS
else return Find( The.Left, I ); --Try LHS
end if;
end if;
end Find;
As the tree is built using dynamic storage, the storage must be released. The procedure Release_Storage
carries out this task:
procedure Dispose is
new Unchecked_Deallocation( Leaf, Subtree );
procedure Release_Storage( The:in out Subtree ) is
begin
if The /= null then --Not empty
Release_Storage( The.Left ); --Free LHS
Release_Storage( The.Right ); --Free RHS
Dispose( The ); --Dispose of item
end if;
The := null;
--Subtree root NULL
end Release_Storage;
end Class_Pic;
Note:
The implicit garbage collector could be used, but this would only be called when the instance of the
class Pic went out of scope. If this object is serially re-used then storage used by the program could
become excessive.
© M A Smith - May not be reproduced without permission