2011-02-19 ArrayList by units and objects in Pascal

2011-02-19 arraylist-by-units-and-objects-in-pascal

# Title: ArrayList by units and objects in Pascal
# Author: Mikael Lundin
# Link: http://blog.mikaellundin.name/2011/02/19/arraylist-by-units-and-objects-in-pascal.html

Collections.pas

unit Collections;
 interface 
  type
   (* Linked List *)
   ListRef = ^List;
   List = record
    current : Pointer; (* Some object *)
    next : ListRef;
    end;
 
   (* Array List Object *)
   ArrayListRef = ^ArrayList;
   ArrayList = object
    first : ListRef;
    last : ListRef;
    constructor Init;
    destructor Done;
    procedure Add(el : Pointer);
    function Empty : boolean;
    function Head : Pointer;
    function Tail : ArrayListRef;
   end;
 
 implementation
  constructor ArrayList.Init;
   begin
    first := nil;
    last := nil;
   end;
 
  (* Free all elements from the linked list *)
  procedure DisposeAll(list : ListRef);
   var next : ListRef;
   begin
    if list <> nil then begin
     next := list^.next;
      Dispose(list); (* Free memory *)
     DisposeAll(next);
    end
   end;
 
  destructor ArrayList.Done;
   begin
    last := nil;
    DisposeAll(first);
    first := nil;
   end;
 
  (* Add element to the list *)
  procedure ArrayList.Add(el : Pointer);
   var item : ListRef;
   begin
    New(item);
    item^.current := el;
     
    if first = nil then
     first := item
    else
     last^.next := item;
     
    last := item;    
   end;
 
  (* Is the list empty? *)
  function ArrayList.Empty : boolean;
   begin
    Empty := first = nil;
   end;
 
  (* First element in list *)
  function ArrayList.Head : Pointer;
   begin
    if Empty then
     Head := nil
    else
     Head := first^.current    
   end;
 
  (* Rest of the list *)
  function ArrayList.Tail : ArrayListRef;
   var list : ArrayListRef;
   begin
    New(list, Init);
 
    list^.first := first^.next;
    list^.last := last;
    Tail := list;
   end;
 end.

RecordStore.pas

program RecordStore;
 uses Collections; (* Import the type ArrayList *)
 
 type
  RecordRef = ^RecordObject;
 
  RecordObject = object
   title : string;
   artist : string;
   constructor Create(titleInput, artistInput : string);
   procedure Print;
  end;
 
 var records : ArrayListRef;
 
 (* RecordObject instance procedures *)
 constructor RecordObject.Create(titleInput, artistInput : string);
  begin
   title := titleInput;
   artist := artistInput;
  end;
 
 procedure RecordObject.Print;
  begin
    Write(title);
    Write(' - ');
    Writeln(artist);
  end;
 
 (* Main program *)
 procedure Add(title, artist : string);
  var my_record : RecordRef;
  begin
   New(my_record, Create(title, artist));
   records^.Add(my_record);
  end;
 
 (* Go through list and print every record *)
 procedure Print(list : ArrayListRef);
  var
   tail : ArrayListRef;
   current : RecordRef;
  begin
   if not list^.Empty then begin
    current := list^.Head;
    current^.Print; (* Print record *)
 
    tail := list^.Tail;
    Print(tail);
    Dispose(tail); (* Disposes the tail, not the records in the list *)
   end;
  end;
 
 begin
  (* Create new list of records *)
  New(records, Init);
 
  Add('Dark side of the moon', 'Pink Floyd');
  Add('The Rise and Fall of Ziggy Stardust and the Spiders from Mars', 'David Bowie');
  Add('L.A. Woman', 'The Doors');
 
  Print(records);
  Dispose(records, Done);
 end.