[swift-users] Callback in Swift

[John Brownie]

Thanks, that does it for me, though I had to qualify the Unmanaged with 
a type in the first part.

Rien wrote:
> For the context I passed in:
>
> UnsafeMutableRawPointer(Unmanaged.passUnretained(self).toOpaque())
>
> And to get the context back inside the callback:
>
> let ourself = Unmanaged<  … your type here…>.fromOpaque(arg!).takeUnretainedValue()
>
> Then “ourself” was the object normally obtained as “self”.
>
A more general question is how to learn these tricks. The worst pain 
I've had in learning Swift is how to handle interactions with frameworks 
in other languages, such as this one (Cocoa) or the Expat parser (C). 
The Swift book doesn't even mention Unmanaged or opaque. The book on 
using Swift with Objective-C mentions Unmanaged, but not opaque (apart 
from a couple of references, neither of which mentions 
toOpaque/fromOpaque. If there were a reference that gathered these 
things together in one place, it would be easier to learn than simply 
thrashing around for a while and asking for help.
-- 
John Brownie
In Finland on furlough from SIL Papua New Guinea