output.txt

2012-08-14 21:37:00.234 TCMemoryTools[10614:303] Todo: overload initWithThing:
2012-08-14 21:37:00.236 TCMemoryTools[10614:303] +[Base @ 0x100003508 allocWithZone:], RC -1
2012-08-14 21:37:00.236 TCMemoryTools[10614:303] -[Child @ 0x102400030 retain], RC 1
2012-08-14 21:37:00.237 TCMemoryTools[10614:303] -[Child @ 0x102400030 release], RC 2
2012-08-14 21:37:00.237 TCMemoryTools[10614:303] -[Child @ 0x102400030 retain], RC 1
2012-08-14 21:37:00.237 TCMemoryTools[10614:303] -[Child @ 0x102400030 release], RC 2
2012-08-14 21:37:00.238 TCMemoryTools[10614:303] Hello, World! <__TCMemoryProxy_Child: 0x102400030>
2012-08-14 21:37:00.238 TCMemoryTools[10614:303] -[Child @ 0x102400030 release], RC 1
2012-08-14 21:37:00.238 TCMemoryTools[10614:303] -[Child @ 0x102400030 dealloc], RC 1

TCMemoryDebugPrinter.h

#import <Foundation/Foundation.h>

@interface TCMemoryDebugPrinter : NSObject
+ (Class)activateMemoryDebuggingFor:(Class)sourceClass;
@end

TCMemoryDebugPrinter.m

#import "TCMemoryDebugPrinter.h"
#import <objc/runtime.h>
#import <objc/message.h>

#define MEMLOG(classorinstance, instance, sel) NSLog(@"%@[%@ @ %p %@], RC %lu", classorinstance, NSStringFromClass([instance superclass]), instance, NSStringFromSelector(sel), (unsigned long)[instance retainCount])

@interface NSObject ()
+ (id)fakeAllocWithZone:(NSZone*)zone;
@end

static dispatch_queue_t proxyMapQueue;
static NSMutableDictionary *proxyMap;

@implementation TCMemoryDebugPrinter
+ (void)initialize
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        proxyMap = [NSMutableDictionary new];
        proxyMapQueue = dispatch_queue_create("TCMemoryProxy.proxyMap", DISPATCH_QUEUE_SERIAL);
    });
}
+ (void)setObject:(id)obj forKey:(id)key;
{
    dispatch_sync(proxyMapQueue, ^{
        [proxyMap setObject:obj forKey:key];
    });
}
+ (id)objectForKey:(id)key;
{
    __block id ret = nil;
    dispatch_sync(proxyMapQueue, ^{
        ret = [proxyMap objectForKey:key];
    });
    return ret;
}

+ (Class)activateMemoryDebuggingFor:(Class)sourceClass;
{
    NSString *sourceClassName = NSStringFromClass(sourceClass);
    Class targetClass = [self objectForKey:sourceClassName];
    if(!targetClass) {
        targetClass = [self makeMemorySubclassFor:sourceClass];
        [self setObject:targetClass forKey:sourceClassName];
    }
    return targetClass;
}

+ (Class)makeMemorySubclassFor:(Class)sourceClass;
{
    NSString *targetClassName = [NSString stringWithFormat:@"__TCMemoryProxy_%@", NSStringFromClass(sourceClass)];
    Class targetClass = objc_allocateClassPair(sourceClass, [targetClassName UTF8String], 0);
    
    {
        SEL sel = sel_registerName("dealloc");
        class_addMethod(targetClass, sel, imp_implementationWithBlock(^void(__unsafe_unretained id me) {
            MEMLOG(@"-", me, sel);
            void(*superIMP)(id, SEL) = (void*)[sourceClass instanceMethodForSelector:sel];
            superIMP(me, sel);
        }), method_getTypeEncoding(class_getInstanceMethod(sourceClass, sel)));
    }
    
    {
        SEL sel = sel_registerName("retain");
        class_addMethod(targetClass, sel, imp_implementationWithBlock(^void(__unsafe_unretained id me) {
            NSLog(@"%@[%@ @ %p %@], RC %lu > %lu", @"-", NSStringFromClass([me superclass]), me, NSStringFromSelector(sel), (unsigned long)[me retainCount], (unsigned long)[me retainCount] + 1);
            void(*superIMP)(id, SEL) = (void*)[sourceClass instanceMethodForSelector:sel];
            superIMP(me, sel);
        }), method_getTypeEncoding(class_getInstanceMethod(sourceClass, sel)));
    }
    
    {
        SEL sel = sel_registerName("release");
        class_addMethod(targetClass, sel, imp_implementationWithBlock(^void(__unsafe_unretained id me) {
            NSLog(@"%@[%@ @ %p %@], RC %lu > %lu", @"-", NSStringFromClass([me superclass]), me, NSStringFromSelector(sel), (unsigned long)[me retainCount], (unsigned long)[me retainCount] - 1);
            void(*superIMP)(id, SEL) = (void*)[sourceClass instanceMethodForSelector:sel];
            superIMP(me, sel);
        }), method_getTypeEncoding(class_getInstanceMethod(sourceClass, sel)));
    }
    
    {
        SEL sel = sel_registerName("autorelease");
        class_addMethod(targetClass, sel, imp_implementationWithBlock(^id(__unsafe_unretained id me) {
            NSLog(@"%@[%@ @ %p %@], RC %lu > %lu later", @"-", NSStringFromClass([me superclass]), me, NSStringFromSelector(sel), (unsigned long)[me retainCount], (unsigned long)[me retainCount] - 1);
            id(*superIMP)(id, SEL) = (void*)[sourceClass instanceMethodForSelector:sel];
            id ret = superIMP(me, sel);
            return ret;
        }), method_getTypeEncoding(class_getInstanceMethod(sourceClass, sel)));
    }
    
    unsigned int methodCount = 0;
    Method *methods = class_copyMethodList(sourceClass, &methodCount);
    for(int i = 0; i < methodCount; i++) {
        Method method = methods[i];
        if([NSStringFromSelector(method_getName(method)) hasPrefix:@"init"]) {
            NSLog(@"Todo: overload %@", NSStringFromSelector(method_getName(method)));
        }
    }
    
    objc_registerClassPair(targetClass);
    
    SEL origSel = sel_registerName("allocWithZone:");
    SEL altSel = sel_registerName("fakeAllocWithZone:");
    Class sourceMetaClass = object_getClass(sourceClass);
    class_addMethod(sourceMetaClass, altSel, imp_implementationWithBlock(^id(__unsafe_unretained id me, NSZone *zone) {
        NSLog(@"+[%@ @ %p %@]", NSStringFromClass(me), me, NSStringFromSelector(origSel));
        id ret = [sourceClass fakeAllocWithZone:zone];
        NSLog(@"+[%@ alloc] yields %@", sourceMetaClass, ret);
        object_setClass(ret, targetClass);
        return ret;
    }), method_getTypeEncoding(class_getClassMethod(sourceClass, origSel)));

    Method origMethod = class_getClassMethod(sourceClass, origSel);
    class_addMethod(sourceMetaClass, origSel, method_getImplementation(origMethod), method_getTypeEncoding(origMethod));
    method_exchangeImplementations(class_getInstanceMethod(sourceMetaClass, origSel), class_getInstanceMethod(sourceMetaClass, altSel));
    
    return targetClass;
}
@end

usage.m

#import <Foundation/Foundation.h>
#import "TCMemoryDebugPrinter.h"

@interface Base : NSObject
- (id)initWithStuff:(id)stuff;
@end
@interface Child : Base
- (id)initWithThing:(id)thing;
@end

@implementation Child
- (id)initWithThing:(id)thing
{
    return [super initWithStuff:thing];
}
- (void)dealloc
{
    
}
+ (id)allocWithZone:(NSZone*)z
{
    return [super allocWithZone:z];
}
@end
@implementation Base {
    id _stuff;
}
- (id)initWithStuff:(id)stuff;
{
    if(!(self = [super init]))
        return nil;
    _stuff = stuff;
    return self;
}
- (void)dealloc
{
    _stuff = nil;
}
@end

int main(int argc, const char * argv[])
{
    @autoreleasepool {
        [TCMemoryDebugPrinter activateMemoryDebuggingFor:[Child class]];
        
        id child = [[Child alloc] initWithThing:@"foo"];
        
        NSLog(@"Hello, World! %@", child);
    }
    return 0;
}