NSObjectAssociativeObject.swift

extension NSObject {
    
    /**
     *  ASSOCIATED - OBJECTS
     */
    public func associate(value: AnyObject, withKey: String) {
        objc_setAssociatedObject(self, withKey, value, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
    }
    
    public func getAssociatedValue(key: String) -> AnyObject {
        return objc_getAssociatedObject(self, key)
    }
}

NSObjectSwizzle.swift

extension NSObject {
    
    struct Static {
        static var onceToken: dispatch_once_t = 0
    }
    
    /**
      Method Swizzling
     
     - parameter className:        name of the class for which swizzling needs to happen
     - parameter originalSelector: originalSelector: method which is already present in the class
     - parameter swizzledSelector: swizzledSelector: new method which will be swizzled with the originSelector
     */
    
    public func swizzleInstanceMethod(className: AnyClass, originalSelector: Selector, swizzledSelector: Selector) {
        
        dispatch_once (&Static.onceToken) {
            let originalMethod = class_getInstanceMethod(className, originalSelector)
            let swizzledMethod = class_getInstanceMethod(className, swizzledSelector)
            
            let didAddMethod = class_addMethod(className, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod))
            
            if didAddMethod {
                class_replaceMethod(className, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod))
            }else {
                method_exchangeImplementations(originalMethod, swizzledMethod)
            }
        }
    }
    
    public func swizzleClassMethod(className: AnyClass, originalSelector: Selector, swizzledSelector: Selector) {
        
        dispatch_once (&Static.onceToken) {
            let originalMethod = class_getClassMethod(className, originalSelector)
            let swizzledMethod = class_getClassMethod(className, swizzledSelector)
            
            let didAddMethod = class_addMethod(className, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod))
            
            if didAddMethod {
                class_replaceMethod(className, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod))
            }else {
                method_exchangeImplementations(originalMethod, swizzledMethod)
            }
        }
    }
}