Dynamic Dispatch with objc protocols

dynamic.swift

import Foundation

@objc
protocol Bimpy: NSObjectProtocol {
  func bimp() -> String
}

@objc
protocol DefaultBimpy: Bimpy {
  func bimp() -> String
}
extension DefaultBimpy {
  func bimp() -> String {
    return "bimped"
  }
}

class Bimper: NSObject, DefaultBimpy {}

func doBimp(bimper: Bimpy) -> String {
  return bimper.bimp()
}

doBimp(Bimper())

/*
2015-12-09 13:26:56.976 Streams[50789:949838] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__lldb_expr_54.Bimper bimp]: unrecognized selector sent to instance 0x7fa0a2e0c640'
*** First throw call stack:
(
	0   CoreFoundation                      0x00007fff93ec0ae2 __exceptionPreprocess + 178
	1   libobjc.A.dylib                     0x00007fff828e3f7e objc_exception_throw + 48
	2   CoreFoundation                      0x00007fff93ec3b9d -[NSObject(NSObject) doesNotRecognizeSelector:] + 205
	3   CoreFoundation                      0x00007fff93dfc412 ___forwarding___ + 514
	4   CoreFoundation                      0x00007fff93dfc188 _CF_forwarding_prep_0 + 120
	5   ???                                 0x000000010767d56a 0x0 + 4419212650
	6   ???                                 0x000000010767d0b3 0x0 + 4419211443
	7   Streams                             0x0000000107022700 main + 0
	8   Streams                             0x0000000107023b31 _TTRXFo__dT__XFo_iT__iT__ + 17
	9   Streams                             0x0000000107023861 _TPA__TTRXFo__dT__XFo_iT__iT__ + 81
	10  Streams                             0x0000000107023bb0 _TTRXFo_iT__iT__XFo__dT__ + 32
	11  Streams                             0x0000000107023be7 _TTRXFo__dT__XFdCb__dT__ + 39
	12  CoreFoundation                      0x00007fff93dd04ac __CFRUNLOOP_IS_CALLING_OUT_TO_A_BLOCK__ + 12
	13  CoreFoundation                      0x00007fff93dc2165 __CFRunLoopDoBlocks + 341
	14  CoreFoundation                      0x00007fff93dc192e __CFRunLoopRun + 910
	15  CoreFoundation                      0x00007fff93dc1338 CFRunLoopRunSpecific + 296
	16  HIToolbox                           0x00007fff8c025935 RunCurrentEventLoopInMode + 235
	17  HIToolbox                           0x00007fff8c025677 ReceiveNextEventCommon + 184
	18  HIToolbox                           0x00007fff8c0255af _BlockUntilNextEventMatchingListInModeWithFilter + 71
	19  AppKit                              0x00007fff8576a0ee _DPSNextEvent + 1067
	20  AppKit                              0x00007fff85b36943 -[NSApplication _nextEventMatchingEventMask:untilDate:inMode:dequeue:] + 454
	21  AppKit                              0x00007fff8575ffc8 -[NSApplication run] + 682
	22  Streams                             0x00000001070229b8 main + 696
	23  libdyld.dylib                       0x00007fff833b45ad start + 1
	24  ???                                 0x0000000000000001 0x0 + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
*/