Func<,> delegates prevent module loading

[Mr Shifty]

I've got the following code in my MonoBehavior derived class:

[COLOR="#0000FF"]private[/COLOR] [COLOR="#40E0D0"]Func[/COLOR]<[COLOR="#40E0D0"]AvailablePart[/COLOR], [COLOR="#0000FF"]bool[/COLOR]> filter;

[COLOR="#0000FF"]private bool[/COLOR] NoAero([COLOR="#40E0D0"]AvailablePart[/COLOR] part)
{
    [COLOR="#0000FF"]return[/COLOR] part.category == [COLOR="#40E0D0"]PartCategories[/COLOR].Aero;
}

[COLOR="#0000FF"]public void[/COLOR] OnGUI()
{
    [COLOR="#0000FF"]if[/COLOR] ([COLOR="#40E0D0"]GUI[/COLOR].Button([COLOR="#0000FF"]new[/COLOR] [COLOR="#40E0D0"]Rect[/COLOR](400, 200, 50, 50), [COLOR="#800000"]"Push Me"[/COLOR]))
    {
        [COLOR="#40E0D0"]Debug[/COLOR].Log([COLOR="#800000"]"Button"[/COLOR]);
        filter = NoAero; [COLOR="#008000"]// PROBLEM LINE[/COLOR]
        [COLOR="#40E0D0"]Debug[/COLOR].Log(filter.ToString());
    }
}

The whole assembly fails to load when the game starts up. (I can see the failure in KSP.log.) If I comment out the problem line, the assembly loads fine. I originally was using a lambda expression in place of the Func instantiation, but when that wasn't working, I whittled the problem down to this. Many of the functions in the KSP assembly require Func predicates or callbacks. How do I use them?

Edit: I'm currently at work and won't be home to make changes/check on proposed fixes/gather and supply more information until this evening. But I'd appreciate any suggestions in the meantime.

Edited June 6, 2013 by Mr Shifty

[EndlessWaves]

Most of the callbacks in KSP are used simply by:

Object.callbackVariable += yourMethodName;

&

Object.callbackVariable -= yourMethodName;

[Mr Shifty]

Most of the callbacks in KSP are used simply by:

Object.callbackVariable += yourMethodName;

&

Object.callbackVariable -= yourMethodName;

This syntax typically only works with events, though Unity might have some strange operator override that uses it for void return type delegates. (I've been coding in C# for over a decade, but the whole Unity "scripting interface grafted into a procedural language" thing is very strange.)

Regardless, I'm using the Func as a predicate (notice it has a bool return type), not a callback, so I can't use that syntax.

[Majiir]

Are you targeting your build at .NET framework 3.5?

[Mr Shifty]

Are you targeting your build at .NET framework 3.5?

No, 4.5. I suppose you're going to tell me that it needs to be 3.5. Thank you. I will try that when I get close to my code again.

[Mr Shifty]

That was the problem. Thanks again Majiir!