How do I do weak linking in Swift?

Question

In Objective-C, if I wanted to use a specific class that\'s only present in a new version of iOS, I would do something like this:

if( [UIBlurEffect class] )          


        

Answer 1

Just to add my two cents since I ended up using this to my immediate dismay upon distributing the app to our testers. There is a bug in the Swift compiler (Xcode <= 6.1.1) whereby when building in Release mode the compiler actually doesn't return nil when calling NSClassFromString.

To check me simply change your configuration to Release and see how she crashes.

I ended up having to explicitly check for iOS versions or a simple respondsToSelector call in other place.

So where my code looked like this:

    if NSClassFromString("UIVisualEffectView") != nil {
        //use the blur safely
    } else {
        //abandon blur! try something safer
    }

I ended up having to use this instead

switch UIDevice.currentDevice().systemVersion.compare("8.0.0", options: NSStringCompareOptions.NumericSearch) {
        case .OrderedSame, .OrderedDescending:
            //go wild with blur
        case .OrderedAscending:
            //blur shall not pass here!
        }

This question dealt with the same issue - UIAlertView is crashing app on iOS 7