Provided by: perl-tk_804.029-1.1ubuntu2_amd64 bug

NAME

       Tcl vs perl - very old suspect documentation on porting.

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 It is also out-of-date in places.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.