Object-oriented Software in Ada 95

Containers 263
• If the objects overlap (share the same storage):
Action on assignment Commentary
Anon := Original; Perform the assignment:
'Anon := Original;'
Adjust(Anon); Increment the reference count for the object
Anon.
Finalize(Copy); Decrement by one the reference count for the
object Copy.
If this is now zero, release the storage that the
object Copy points to.
Copy := Anon; Perform the assignment:
'Copy := Original;'
Adjust(Copy); Increment the reference count for the object
Copy.
Finalize(Anon); Decrement by one the reference count for the
object Anon.
If this is now zero release the storage that the
object Anon points to.
• If the objects do not overlap, the following optimization may be performed:
Action on assignment Commentary
Finalize(Original); Decrement by one the reference count for the
object Original.
If this is now zero, release the storage that the
object Original points to.
Copy := Original; Perform the assignment:
'Copy := Original;'
Adjust(Copy); Increment the reference count for the object
Copy.
Note:
The compiler may generate no code if the target and the source are the same.
When a reference counted item is passed as a parameter to a function or procedure by value, for example:
Procedure
Call of procedure
procedure Put(L:in List) is
begin
....
end Put;
declare
Colours : List;
Begin
Put( Colours );
end;
then only the following actions are performed:
Put( Colours )
L := Colours;
Adjust(L);
Commentary
Perform the assignment of colours to the
formal parameter:
'L := colours;'
Increment the reference count for the actual
parameter L.
Note: When the procedure put is exited, finalize will be called on the formal parameter l.
© M A Smith - May not be reproduced without permission