Madness.

ex.m

@interface Sender : NSObject
@property (weak) id delegate;
@property (assign) SEL selector;
- (void)doSth;
@end

@interface Receiver : NSObject
@property (strong) Sender* whatever;
@property (copy) void(^blockStuff)();
- (void)assumeThisIsRun;
@end


@implementation Sender
@synthesize delegate=_delegate;
@synthesize selector=_selector;
- (void)doSth
{
  [_delegate performSelector:_selector];
}
@end

@implementation Receiver
@synthesize whatever=_whatever;
@synthesize blockStuff=_blockStuff;
- (void)assumeThisIsRun
{
  self.whatever = [[Sender alloc] init];
  self.blockStuff = ^{NSLog(@"Hello world!");};
  _whatever.delegate = _blockStuff;
  _whatever.selector = @selector(startBlock);
  [_whatever doSth];
}
@end