Re: Re: transparent proxy using forwardInvocation, how?

FROM : Simon Strandgaard
DATE : Sat Aug 26 19:57:09 2006

On 8/26/06, Julien Jalon <<email_removed>> wrote:
> On 8/26/06, Nick Zitzmann <<email_removed>> wrote:
> >
> > On Aug 26, 2006, at 3:23 AM, Simon Strandgaard wrote:
> >
> > > How does one make a transparent proxy?
> >
> > Subclassing NSProxy and overriding -forwardInvocation: ought to work...

[snip]


Ok, I am now inheriting from NSProxy... code is below.



[snip]
> Some notes about NSProxy:
> 1) don't need to call [super init] (NSProxy has no init'er...)
> 2) also implement:
> - methodSignatureForSelector:
> - conformsToProtocol:
> - and, if you want to, respondsToSelector:



I have just seen Julien's reply.. I am about to leave my computer for
some hours.
I see that I need to impl comformsToProtocol and respondToSelector.


If I don't override class:  (and superclass: as well) then I an exception
when I invoke [obj class].  Should'nt this be forwarded through the proxy?
*** Uncaught exception: <NSInvalidArgumentException> *** -[NSProxy
methodSignatureForSelector:] called!


Are these methods enough to do a transparent proxy?
methodSignatureForSelector:
forwardInvocation:
comformsToProtocol:
respondToSelector:



--
Simon Strandgaard

// main.mm
#include <Foundation/Foundation.h>

@interface TransparentProxy : NSProxy {
   id _proxied_object;
}
@end

@implementation TransparentProxy

-(id)initWithProxiedObject:(id)object {
   NSLog(@"[proxy.init]\n");
   _proxied_object = object;
   return self;
}

-(NSMethodSignature*)methodSignatureForSelector:(SEL)sel {
   NSLog(@"[proxy.msfs] methodSignatureForSelector \"%@\"\n",
       NSStringFromSelector(sel));
   
   NSMethodSignature* sig = nil;
   sig = [_proxied_object methodSignatureForSelector:sel];
   if(sig) {
       NSLog(@"[proxy.msfs] recognized by proxied_object\n");
       return sig;
   }

   sig = [NSObject methodSignatureForSelector:@selector(self)];
   NSLog(@"[proxy.msfs] ERROR: selector not recognized, absorbing!\n");
   return sig;
}

-(void)forwardInvocation:(NSInvocation*)inv {
   SEL sel = [inv selector];
   NSLog(@"[proxy.fi] forwardInvocation \"%@\"\n",
       NSStringFromSelector(sel));
       
   if([_proxied_object respondsToSelector:sel]) {
       NSLog(@"[proxy.fi] invoking with proxy\n");
       [inv invokeWithTarget:_proxied_object];
       return;
   }
   NSLog(@"[proxy.fi] ERROR: absorbing!\n");
}

-(Class)class {
   NSLog(@"[proxy.class]\n");
   return [_proxied_object class];
}

-(Class)superclass {
   NSLog(@"[proxy.superclass]\n");
   return [_proxied_object superclass];
}
@end

int main(int argc, char *argv[]) {
   NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init];

   NSNumber* num = [[NSNumber alloc] initWithInt:42];
   id obj = [[TransparentProxy alloc] initWithProxiedObject:num];
   NSLog(@"---------------\n");
   
   NSLog(@"[obj xintValue]\n");
   int i = [obj xintValue];
   NSLog(@"i=%i\n", i);
   NSLog(@"---------------\n");
   
   NSLog(@"[obj setValue:5]\n");
   [obj setValue:5];
   NSLog(@"---------------\n");

   NSLog(@"[obj intValue]\n");
   int j = [obj intValue];
   NSLog(@"j=%i\n", j);
   NSLog(@"---------------\n");
   
   NSLog(@"instance=%@\n", obj);
   NSLog(@"---------------\n");

   NSLog(@"class=%@\n", [obj class]);
   NSLog(@"---------------\n");

   NSLog(@"superclass=%@\n", [obj superclass]);
   NSLog(@"---------------\n");
   
   NSLog(@"[obj self]\n");
   NSLog(@"self=%@\n", [obj self]);
   NSLog(@"---------------\n");
   
   NSLog(@"[obj respondsToSelector:@selector(dontUnderstand)];\n");
   [obj respondsToSelector:@selector(dontUnderstand)];
   NSLog(@"---------------\n");

   NSLog(@"[obj performSelector:@selector(dontUnderstand)];\n");
   [obj performSelector:@selector(dontUnderstand)];
   NSLog(@"---------------\n");
   
   NSLog(@"[obj isKindOfClass: [NSCell class]];\n");
   BOOL b1 = [obj isKindOfClass: [NSCell class]];
   NSLog(@"is same: %s\n", (b1 ? "yes" : "no"));
   NSLog(@"---------------\n");

   NSLog(@"[obj isKindOfClass: [NSNumber class]];\n");
   BOOL b2 = [obj isKindOfClass: [NSNumber class]];
   NSLog(@"is same: %s\n", (b2 ? "yes" : "no"));
   NSLog(@"---------------\n");
   
   return 0;
}