Re: [TCLCORE] Tcl GSoC 2011 - Ideas anyone ? [Tk]

On 3/15/2011 8:45 PM, Kevin Walzer wrote:
> That's a key point> in Tk's favor--it's so easy to extend. Extending wxWidgets is a lot> harder, and I imagine that extending Qt would be even harder. That's> ultimately why I stay with Tk.

I have a lot of experience extending Qt, though it's been a year or two 
since I've done any Qt work.  Extending Qt requires C++ subclassing. 
Giving a widget behavior often requires subclassing (though signals and 
slots may work too, more on that later).  Making a dialog in Qt is like 
making a megawidget; subclass the QDialog or QWindow class (or whatever 
it's called) and put in code to create, configure, bind, and position 
the interior widgets.  There's a program called Designer that generates 
this code for you, though I prefer to do it by hand when management permits.

It's not quite as bad as you'd expect, since only a subset of C++ is 
used.  Exceptions are never used.  I don't recall virtual or diamond 
inheritance either.  Templates are rare.  In fact, I think the Qt 
approach to C++ is a good illustration of what's wrong with C++.  In 
many ways, it uses C++ in a manner that makes it more like C.  For 
example, the class definitions rarely contain private members; instead 
they contain what's called a "d pointer" that points to a separate 
structure containing the private stuff.  This is the C++ analog of C's 
incomplete structs.

So I've talked about using C++ to extend Qt.  But did you know that Qt 
extends C++?  It uses a mechanism called signals and slots to do event 
notification.  Slots are programmer-written functions that receive 
events as arguments.  Signals are MOC-generated functions that consult 
the connection tables and call all the currently connected slot 
functions.  Signal/slot connections are dynamically established using 
the connect() and disconnect() functions.  MOC is the Qt Meta-Object 
Compiler.  It scans your source code to find special Qt keywords such as 
signal and slot, which the C++ compiler ignores 'cuz they're #defined 
away, then generates code based on what it finds.

All this together made me wonder how to possibly make a Tcl binding for 
Qt.  Maybe there's some Tcl/C black magic that can take the place of the 
C++ subclassing and code generation required by Qt, but it's beyond me.

-- 
Andy Goth | <andrew.m.goth/at/gmail/dot/com>

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