Callback to Lua member function

Question

I have a lua "animation variable" which has a callback function used in an animation loop.

local av = AnimationVariable(ticker.Position.Y)
...
av:addCallback( ** animation function goes here **)

Skipping over details, this addCallback function is defined as follows in C++:

void LuaUIAnimationVariable::addCallback(luabind::object callback);

and when the animation variable is updated, the callback is executed as such (we call the function with one argument):

luabind::call_function<void>(boost::ref(callback), newValue);

My question is the following: How can I use a member function with addCallback? Assuming I have a Ticker:animate(ypos) function, using addCallback on a Ticker instance addCallBack(ticker:animate) does not compile, and addCallBack(ticker.animate) does not work. I understand that member functions in lua have an implicit "self" first parameter.

Any solution or am I forced to use a global function?

Seth Carnegie · Accepted Answer · 2012-07-17 19:57:30Z

4

Not sure if I understand your question, but if you mean a Lua member function, you can use a closure:

av:addCallback(function(yval) ticker:animate(yval) end)

answered Jul 17, 2012 at 19:57

Seth Carnegie

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4 Comments

num3ric Over a year ago

This assumes that ticker is global, doesn't it? Problem is addCallback is inside a for-loop which goes through all my tickers.

furq Over a year ago

It only assumes that ticker is within scope; whatever ticker refers to at the time the closure is created is what it will refer to whenever you call it.

Seth Carnegie Over a year ago

@num3ric that's why they call it a closure. It captures the variable at the time it's created and remains unaffected if you assign to the variable outside the closure.

Nicol Bolas Over a year ago

@furq: "whatever ticker refers to at the time the closure is created is what it will refer to whenever you call it." That's only true if it is a local variable. If ticker is global, then it will attempt to access the global variable every time the function is called. Lua closures only close over local variables.

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