Re: [RFA] New Event Model Prototype

[Keith Seitz <keiths at cygnus dot com>]

On Mon, 16 Apr 2001, Jim Ingham wrote:

> I have another question about this.  How were you planning to pass all 
> the details about the event?  Will there be methods in the GDBEvent 
> class to get out the event data?  It almost seems like you want to have:
> 
> GDBEvent
>      |
>      ------> BreakpointEvent
>      |
>      ------> ExecutionStateEvent
> 
> and ALL you ever pass to the dispatch method is an event of the 
> appropriate class.  This would really simplify the code in the event 
> listeners, and we wouldn't get into the situation of the current code, 
> where the event handlers have to know the order of the parameters in the 
> hook call, which is very fragile.

I agree with you guys that we would like to NOT have to pass a huge list 
of arguments to the handles, but I'm not sure that this is going to work 
in Itcl anywhere as cleanly as it does in C++. 

So, the proposal is to add some Event classes (which will essentially all 
be arrays of data??). Bear with me here... read the whole thing 
before responding...

Something like:

class GdbEvent {

  protected variable _type "unknown"

  public {
    proc dispatch {} {
      foreach w [itcl_info objects -isa EVENTLISTENER] {
        catch {$w $_type $this}
      }
    }
  }
}

class FooEvent {
  inherit GdbEvent

  public {
    constructor {args} {
      set _type foo
      eval configure $args
    }

    variable varA
    variable varB
    variable varC
    variable varD
  }
}

proc gdbtk_tcl_foo_event {varA varB varC varD} {
  set e [FooEvent #auto -varA $varA -varB $varB -varC $varC -varD $varD]
  $e dispatch
  delete object $e
}

And this would call the "foo" method of every EVENTLISTENER object with 
the object as an argument. So something listening for FooEvent would look 
like:

class MyObject {
  inherit EVENTLISTENER

  public {
    method foo {event} {
      puts "varA = [$event cget -varA]"
      puts "varB = [$event cget -varB]"
      puts "varC = [$event cget -varC]"
      puts "varD = [$event cget -varD]"
    }
  }
}

OR the proposal is to do something like:

class GdbEvent {
  public method type {} { return "unknown" }
}

class FooEvent {
  public method type {} { return "foo" }
}

proc GdbEvent::dispatch {event} {
  set type $event type

  foreach w [itcl_info object -isa GdbEventListener] {
    catch {$w $type $event}
  }
}

class MyObject {
  inherit GdbEventListener

  public method foo {fooEvent} {
    puts "varA = [$fooEvent cget -varA]"
    puts "varB = [$fooEvent cget -varB]"
    puts "varC = [$fooEvent cget -varC]"
  }
}

Are either of these on target? 

Happily, both of these address a big concern: we are constantly asking 
for the same information. Now we'll have an event object to contain it 
all.

Originally, I was going to do this all with arrays, eg. event(type) = 
breakpoint, event(line) = 31, event(file) = /foo/bar/baz, etc. This way, we 
can collect the info once and everyone gets to use it. But I hadn't 
planned on making such a huge change to start with. I guess this is a 
request to do so. ;-)

My itcl is really fuzzy nowadays (having been corrupted by C++), so 
please excuse my C++-ish approaches...

Keith