Howto:Troubleshooting Nasal Callbacks: Difference between revisions

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Howto:Troubleshooting Nasal Callbacks (view source)

Revision as of 21:48, 31 January 2016

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== Motivation ==
{{FGCquote
|1= Someone recently pointed out that the setlistener() / removelistener() API makes it easy to leak resources. So I wondered about making an alternate API where the return value from setlistener '''must''' be kept, or the listener is removed. I can imagine this with a helper object
<syntaxhighlight lang="nasal">
var myL = setlistener2("some/prop", func { ... }} )
myL.addprop("some/other/prop");
myL.addprop("yet/another/prop");
</syntaxhighlight>
Now you need to retain a ref to myL or the listeners on all the props are removed. I don't think we can retro-fit this to the existing API, because I suspect many places just ignore the return value and would break with this change.
(Or even pass a vec of property names to setlistener2, to avoid all the discrete calls to 'addprop', that's a seperate detail really)
It seems like this would work, and be easy enough to implement - question is if it gives enough benefit to be worth the confusion.
|2= {{cite web
  | url    = http://forum.flightgear.org/viewtopic.php?p=192767#p192767
  | title  = <nowiki>Listener objects</nowiki>
  | author = <nowiki>zakalawe</nowiki>
  | date  = Oct 28th, 2013
  }}
}}
== Background ==
== Background ==
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{{FGCquote
|1= Someone recently pointed out that the setlistener() / removelistener() API makes it easy to leak resources. So I wondered about making an alternate API where the return value from setlistener '''must''' be kept, or the listener is removed. I can imagine this with a helper object
<syntaxhighlight lang="nasal">
var myL = setlistener2("some/prop", func { ... }} )
myL.addprop("some/other/prop");
myL.addprop("yet/another/prop");
</syntaxhighlight>
Now you need to retain a ref to myL or the listeners on all the props are removed. I don't think we can retro-fit this to the existing API, because I suspect many places just ignore the return value and would break with this change.
(Or even pass a vec of property names to setlistener2, to avoid all the discrete calls to 'addprop', that's a seperate detail really)
It seems like this would work, and be easy enough to implement - question is if it gives enough benefit to be worth the confusion.
|2= {{cite web
  | url    = http://forum.flightgear.org/viewtopic.php?p=192767#p192767
  | title  = <nowiki>Listener objects</nowiki>
  | author = <nowiki>zakalawe</nowiki>
  | date  = Oct 28th, 2013
  }}
}}


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