Suggestion: signal/slot mechanism

Brad Anderson brad at dsource.org
Sat Sep 2 15:41:55 PDT 2006


Kristian wrote:
> It would be nice if D had a signal/slot mechanism similiar to Qt:
> http://doc.trolltech.com/4.1/signalsandslots.html
> 
> It's an elegant way to handle messages sent between objects. It beats
> event table declarations used by other GUI libraries IMHO.
> 
> It would make D a lot more appealing language to write GUI applications.
> Think of wxWidgets written in D... ;)
> 
> 
> I think it would be quite simple to build a S/S support for a compiler
> (at first glance, at least). For example:
> 
> The 'Object' class has a pointer to S/S data (it's null if the object
> don't currently use signals/slots). S/S data holds a slot list for each
> signal. It also holds a list of objects that have slot(s) connected to
> this object's signal(s). This list is used to disconnect necessary slots
> at a destruction of the object.
> 
> When the compiler reads a 'emit X' statement, it will do two things.
> First, it generates an id for the signal which is used to retrieve a
> correct slot list.
> 
> Second, the compiler puts the signal's parameters to the stack as it
> would call a corresponding function. Instead, the
> 'Object._emit_signal(id)' function (or something) is called, where 'id'
> is the generated id. (Note that there are no function bodies for
> signals.) '_emit_signal()' retrieves the correct slot list, and calls
> all the slots (delegates) in it. Finally the parameters are removed from
> the stack.
> 
> Of course, slots should not modify their parameters so that all the
> slots will receive the same parameter values. Hence slots should not use
> the 'out type'. There is a market for a 'const type' here... *wink*
> 
> 
> Maybe there should be no slot keyword at all as there is in Qt. You
> don't need to declare a function to be a slot; all the (virtual)
> functions can be used with signals.
> 
> Because the return values of all the signals are void, the void typeword
> could be removed from signal declarations.
> 
> signal clicked();
> 
> signals:
> clicked();
> clicked(int button);
> 
> 
> BTW, Qt generates ids for signals as follows:
> 
> signals:
> void clicked(int button, bool isMoved);
> -> the id is a string "clicked(int,bool)"

Not terribly active recently, but the SVN repos here may have some stuff for you.

http://svn.dsource.org/projects/dcouple/

BA



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