Singleton模式之Delphi实现

type
  tsingleton = class(tobject)
  public
    a : integer;
    class function newinstance: tobject; override;
    procedure freeinstance; override;
    class function refcount: integer;
  end;

implementation

var
  instance  : tsingleton  = nil;
  ref_count : integer     = 0;

procedure tsingleton.freeinstance;
begin
  dec( ref_count );
  if ( ref_count = 0 ) then
  begin
    instance := nil;
    // destroy private variables here
    inherited freeinstance;
  end;
end;

class function tsingleton.newinstance: tobject;
begin
  if ( not assigned( instance ) ) then
  begin
    instance := inherited newinstance as tsingleton;
    // initialize private variables here, like this:
    tsingleton(instance).a :3d 1;
  end;
  result := instance;
  inc( ref_count );
end;

class function tsingleton.refcount: integer;
begin
  result := ref_count;
end;