In this quick lighting talk from the 2017 Dot.Swift conference in Paris, I covered one little trick to allow your swift code to add a handy dynamic feature to your code.

1. Dynamic Swift
Saul Mora
@casademora
saul.mora@liulishuo.com

2. •dynamic
•@objc
•NSObject

3. Objective C Runtime
-(BOOL) resolveInstanceMethod:(SEL)aSelector
-(id) forwardingTargetForSelector:(SEL)aSelector
-(NSMethodSignature *) methodSignatureForSelector:(SEL)aSelector
-(void) forwardInvocation:(NSInvocation *)anInvocation

4. Target/Action

5. Method Swizzling

6. Responder Chain

7. Responder Chain

8. "I want something that works like
the responder chain…"

9. let first = FirstHandlerType()
let second = SecondHandlerType(next: first)
let third = ThirdHandlerType(next: second)

10. class Operation: NSObject
{
let nextOperation: Operation?
init(next: Operation? = nil)
{
self.nextOperation = next
}
override func forwardingTarget(for aSelector: Selector!) -> Any?
{
print(String(describing: self))
return nextOperation
}
}

11. third.doSomething()

12. Playground execution failed: error: Dynamic Swift.playground:35:1: error:
value of type 'ThirdHandlerType' has no member 'doSomething'
third.doSomething()
^~~~~ ~~~~~~~~~~~
* thread #1: tid = 0x61b09, 0x000000010f3713c0 Dynamic
Swift`executePlayground, queue = 'com.apple.main-thread', stop reason =
breakpoint 1.2
* frame #0: 0x000000010f3713c0 Dynamic Swift`executePlayground
frame #1: 0x000000010f3709c0 Dynamic Swift`__37-[XCPAppDelegate
enqueueRunLoopBlock]_block_invoke + 32
frame #2: 0x000000010fe8c6ac
CoreFoundation`__CFRUNLOOP_IS_CALLING_OUT_TO_A_BLOCK__ + 12
frame #3: 0x000000010fe716f4 CoreFoundation`__CFRunLoopDoBlocks + 356
frame #4: 0x000000010fe70e65 CoreFoundation`__CFRunLoopRun + 901
frame #5: 0x000000010fe70884 CoreFoundation`CFRunLoopRunSpecific + 420
frame #6: 0x000000011539ba6f GraphicsServices`GSEventRunModal + 161
frame #7: 0x0000000111b07c68 UIKit`UIApplicationMain + 159
frame #8: 0x000000010f3706e9 Dynamic Swift`main + 201
frame #9: 0x00000001134e568d libdyld.dylib`start + 1
frame #10: 0x00000001134e568d libdyld.dylib`start + 1
FAIL

13. One Weird Trick…!

14. let third: AnyObject = ThirdHandlerType(next: second)

15. <__lldb_expr_86.ThirdHandlerType:
0x608000034f60>
<__lldb_expr_86.SecondHandlerType:
0x608000034ec0>
Did: <__lldb_expr_86.FirstHandlerType:
0x600000033080>

16. http://tinyurl.com/
dynamicswiftdemo

17. Dynamic Swift
Saul Mora
@casademora
saul.mora@liulishuo.com