Swift function swizzling / runtime

Question

Before Swift, in Objective-C I would swizzle or hook methods in a class using .

If anyone has any info on the topic of modifying S

Answer 1

I would like to extend the great answer provided by mbazaliy.

Another way of doing swizzling in Swift is by providing an implementation using an Objective-C block.

e.g. to replace descriptionmethod on class NSString we can write:

let originalMethod = class_getInstanceMethod(NSString.self, "description")

let impBlock : @objc_block () -> NSString =
        { () in return "Bit of a hack job!" }

let newMethodImp = imp_implementationWithBlock(unsafeBitCast(impBlock, AnyObject.self))

method_setImplementation(originalMethod, newMethodImp)

This works as of Swift 1.1.