DATELINK unit

A TP 5.5 OOP unit for keeping track of dates

Rob Rosenberger CIS: 74017,1344
Barn Owl Software VOX: (618) 632-7345
P.O. Box #74 BBS: (618) 398-5703
O'Fallon, IL 62269 HST: (618) 398-2305

This unit provides a heap-managed linked list object (OOP)
which keeps track of any number of dates in sorted order. It was
originally set up to store dates corresponding to holidays but,
because of the nature of OOP, you can use DateLink variables to
keep track of multiple linked lists of dates for any purpose.

The DateLink unit builds on the OBJECTS.PAS unit from disk
#3 of the TP 5.5 master disk set, the OBJECTA.PAS unit available
on CompuServe in the BPROGA forum, LIB 1, filename OBJA.ARC, and
on the TpDate unit supplied by TurboPower Software in their TPRO5
toolkit. (OBJECTS.PAS and TpDate are copyrighted works.)

The DateLink unit requires DATEOBJ.PAS, another unit that
builds on OBJECTS.PAS. The DateObj source should be kept in the
same directory with the DateLink source. DateObj is transparent
to the programmer -- DateLink is the one that does all the work
for you. Therefore, DateObj's capabilities are beyond the scope
of this documentation.


Version 1.00: released to the public domain on 8 July 1989.




TYPE
DateLinkList
= OBJECT(LinkList)
CurrentDatePtr : DateObjectPtr;

CONSTRUCTOR Init;
PROCEDURE AddDate(TheDate : Date);
PROCEDURE DeleteDate(TheDate : Date);
FUNCTION Exists(TheDate : Date) : BOOLEAN;
FUNCTION CurrentDate : Date;
FUNCTION FirstDate : Date;
FUNCTION LastDate : Date;
PROCEDURE Advance;
END;


CONSTRUCTOR DateLinkList.Init;

This procedure initializes the DateLinkList variable. The
Done destructor (inherited) should be used to free up the heap
space associated with the list.


PROCEDURE DateLinkList.AddDate(TheDate : Date);

This procedure stores TheDate in the list. It does nothing
if TheDate already exists on the list.


PROCEDURE DateLinkList.DeleteDate(TheDate : Date);

This procedure deletes TheDate from the list. It does
nothing if TheDate doesn't exist on the list.


FUNCTION DateLinkList.Exists(TheDate : Date) : BOOLEAN;

This function determines if the date exists on the list.


FUNCTION DateLinkList.CurrentDate : Date;

The DateLinkList variable type keeps a pointer to what it
knows to be the "current" date. This lets the Advance function
move on to the next date without the programmer having to worry
about it. The FirstDate function initializes CurrentDate; so you
can then use the Advance function to get successive dates on the
list. CurrentDate returns BadDate (defined in TPRO5 TpDate) if
you advance beyond the last date on the list.


FUNCTION DateLinkList.FirstDate : Date;

This function simply returns the first date in the list.
Remember, the list is sorted in ascending order by date. BadDate
(defined in TPRO5 TpDate) is returned if there are no dates on
the list. CurrentDate will return the same date after you call
this function.


FUNCTION DateLinkList.LastDate : Date;

This function simply returns the last date in the list.
Remember, the list is sorted in ascending order by date. BadDate
(defined in TPRO5 TpDate) is returned if there are no dates on
the list. CurrentDate will return the same date after you call
this function.


PROCEDURE DateLinkList.Advance;

This procedure advances the current-date pointer to the next
date in the list. Use the CurrentDate function to find out the
current date. If you advance past the last date on the list, the
CurrentDate function will return with BadDate (defined in TPRO5
TpDate).