=head1 NAME

Tcl_vs_perl - very old suspect documentation on porting.

=for category Other Modules and Languages

=head1 DESCRIPTION

This isn't really a .pod yet, nor is it Tcl vs perl
it is a copy of John's comparison of Malcolm's original perl/Tk
port with the current one. It is also out-of-date in places.

  From: john@WPI.EDU (John Stoffel )

  Here are some thoughts on the new Tk extension and how I think the
  organization of the commands looks.  Mostly, I'm happy with it, it
  makes some things more organized and more consistent with tcl/tk, but
  since the overlying language is so different, I don't think we need to
  follow exactly the tcl/tk model for how to call the language.

  The basic structure of the Tk program is:

      require Tk;

      $top = MainWindow->new();

      #
      # create widgets
      #

      Tk::MainLoop;

      sub method1 {
      }

      sub methodN {
      }

  This is pretty much the same as tkperl5a5, with some cosmetic naming
  changes, and some more useful command name and usage changes.  A quick
  comparison in no particular order follows:

  tkperl5a5				Tk
  -------------------------------	-----------------------------------
  $top=tkinit(name,display,sync);	$top=MainWindow->new();

  tkpack $w, ... ;		$w->pack(...)

  $w = Class::new($top, ...);	$w = $top->Class(...);

  tkmainloop;			Tk::MainLoop;

  tkbind($w,"<key>",sub);		$w->bind("<key>",sub);

  tkdelete($w, ...);		$w->delete(...);

  $w->scanmark(...);		$w->scan("mark", ...);

  $w->scandragto(...);		$w->scan("dragto", ...);

  $w->tkselect();			$w->Select();

  $w->selectadjust(...);		$w->selection("adjust", ...);

  $w->selectto(...);		$w->selection("to", ...);

  $w->selectfrom(...);		$w->selection("from", ...);

  $w->tkindex(...);		$w->index(...);

  tclcmd("xxx",...);              &Tk::xxx(...)    # all Tk commands, but no Tcl at all

  tclcmd("winfo", xxx, $w, ...);  $w->xxx(...);

  				$w->mark(...);

  				$w->tag(...);

  $w->grabstatus();		$w->grab("status");

  $w->grabrelease(...);		$w->grab("release", ...);

  focus($w);			$w->focus;

  update();			Tk->update();

  idletasks();			Tk->update("idletasks");

  wm("cmd",$w, ...);		$w->cmd(...);

  destroy($w);			$w->destroy();

  				Tk::option(...);
                                  $w->OptionGet(name,Class)

  				$w->place(...)

  				Tk::property(...);

  $w = Entry::new($parent,...)

  is now

  $w = $parent->Entry(...)

  As this allows new to be inherited from a Window class.

    -method=>x,-slave=>y

   is now

    -command => [x,y]

  1st element of list is treated as "method" if y is an object reference.
  (You can have -command => [a,b,c,d,e] too; b..e get passed as args).

  Object references are now hashes rather than scalars and there
  is only ever one such per window.  The Tcl_CmdInfo and PathName
  are entries in the hash.

  (This allows derived classes to
  re-bless the hash and keep their on stuff in it too.)

  Tk's "Tcl_Interp" is in fact a ref to "." window.
  You can find all the Tk windows descended from it as their object
  references get added (by PathName) into this hash.
  $w->MainWindow returns this hash from any window.

  I think that it should extend to multiple tkinits / Tk->news
  with different Display's - if Tk code does.

  Finally "bind" passes window as "extra" (or only)
  argument. Thus

  Tk::Button->bind(<Any-Enter>,"Enter");

  Binds Enter events to Tk::Button::Enter by default
  but gets called as $w->Enter so derived class of Button can just
  define its own Enter method. &EvWref and associated globals and race
  conditions are no longer needed.

  One thing to beware of : commands bound to events with $widget->bind
  follow same pattern, but get passed extra args :

  $widget->bind(<Any-1>,[sub {print shift}, $one, $two ]);

  When sub gets called it has :

     $widget $one $two

  passed.

  1st extra arg is reference to the per-widget hash that serves as the
  perl object for the widget.

  Every time an XEvent a reference to a special class is placed
  in the widget hash. It can be retrieved by $w->XEvent method.

  The methods of the XEvent class are the
  Tcl/Tk % special characters.

  Thus:

  $widget->bind(<Any-KeyPress>,
                sub {
                 my $w = shift;
                 my $e = $w->XEvent;
                 print $w->PathName," ",$e->A," pressed ,$e->xy,"\n");
                });

  XEvent->xy is a special case which returns "@" . $e->x . "," . $e->y
  which is common in Text package.

  Because of passing a blessed widget hash to "bound" subs they can be
  bound to (possibly inherited) methods of the widget's class:

  Class->bind(<Any-Down>,Down);

  sub Class::Down
  {
   my $w = shift;
   # handle down arrow
  }

  Also:

  -command and friends can take a list the 1st element can be a ref to
  as sub or a method name. Remaining elements are passed as args to the
  sub at "invoke" time. Thus :

  $b= $w->Button(blah blah, '-command' => [sub{print shift} , $fred ]);

  Should do the trick, provided $fred is defined at time of button creation.

  Thus 1st element of list is equivalent to Malcolm's -method and second
  would be his -slave.  Any further elements are a bonus and avoid
  having to pass ref to an array/hash as a slave.

=cut

