Question

I have no idea if this is possible, but if it is, what would the syntax look like?

If not possible, why not?

Answer 1

You should be able to bind to a message implementation (IMP), which are just plain C functions with two hidden parameters, self and _cmd of types id and SEL respectively.

EDIT: Just tested the following complete example, and it appears to work.

#include <stdio.h>
#include <boost/bind.hpp>
#include <Foundation/NSObject.h>

@interface MyClass : NSObject
{
}
-(int) doSomething:(int)arg;
@end

@implementation MyClass
-(int) doSomething:(int)arg
{
  printf("doSomething: self=0x%08x _cmd=0x%08x\n", self, _cmd);
  return arg + 1;
}
@end

int main(void)
{
  MyClass *myObj = [[MyClass alloc] init], *otherObj = [[MyClass alloc] init];
  typedef int (*MyFunc)(id, SEL, int);
  SEL doSomething_sel = @selector(doSomething:);
  MyFunc doSomething_impl = (MyFunc)[myObj methodForSelector:doSomething_sel];

  // bind self & _cmd arguments:
  // calls [myObj doSomething:x]
  int result = boost::bind(doSomething_impl, myObj, doSomething_sel, _1)(14);
  printf("result1: %d\n", result);

  // bind _cmd & arg:
  // calls [otherObj doSomething:3]
  result = boost::bind(doSomething_impl, _1, doSomething_sel, 42)(otherObj);
  printf("result2: %d\n", result);

  return 0;
}

With GNUstep, compile as:

gcc objcbind.mm -o objcbind -I/usr/include/GNUstep -lobjc -lstdc++ -lgnustep-base

On Mac OS X, compile as:

gcc objcbind.mm -o objcbind -framework Foundation -lstdc++

Output:

doSomething: self=0x01a85f70 _cmd=0x00602220
result1: 15
doSomething: self=0x01a83d70 _cmd=0x00602220
result2: 43