TCObject.m

//
//  TCObject.m
//
//
//  Created by Karsten Kusche on 19.12.20.
//  Copyright © 2020 briksoftware.com. All rights reserved.
//
//
// compile with -fno-objc-arc
//
// This code changes +alloc so that it initializes all inst-vars that have the type <id> to not be <nil> but [TCNull null]
// TCNull prints a Stack-Dump when a message is sent to it, that it doesn't understand. <nil> would silently return nil
// <nil> receivers are typically an indication of missing initialization and the error manifests a lot later
// with this fix it'll crash as soon as someone sends a message to an uninitialized variable
//
// don't use in production code, but during development it's sure helpful
//

#import "TCObject.h"
#import <objc/objc-runtime.h>

@interface TCNull : NSObject

+ (instancetype)null;

@end

Method orgAlloc = nil;

@implementation TCObject

+ (instancetype)tcAlloc
{
	// only handle TC* classes. System classes don't play well with this idea
	const char* name = class_getName(self);
	if (name[0] == 'T' && name[1] == 'C')
	{
		IMP alloc = method_getImplementation(orgAlloc);
		SEL allocSel = method_getName(orgAlloc);
		TCObject* object = ((id(*)(id,SEL))alloc)(self,allocSel);
		unsigned int outCount = 0;
		Ivar* ivars = class_copyIvarList(self, &outCount);
		for (NSInteger i = 0; i < outCount; i++)
		{
			Ivar ivar = ivars[i];
			const char* type = ivar_getTypeEncoding(ivar);
			if (*type == '@')
			{
				object_setIvar(object, ivar, [TCNull null]);
			}
		}
		free(ivars);
		return object;
	}
	else
	{
		IMP alloc = method_getImplementation(orgAlloc);
		SEL allocSel = method_getName(orgAlloc);
		return ((id(*)(id,SEL))alloc)(self,allocSel);
	}
}

+ (void)load
{
	@autoreleasepool {
		[TCNull null];
		[self swizzle];
	}
}

+ (void)swizzle
{
	Method alloc = class_getClassMethod(NSObject.class, @selector(alloc));
	Method tcAlloc = class_getClassMethod(self, @selector(tcAlloc));
	orgAlloc = tcAlloc;
	method_exchangeImplementations(alloc, tcAlloc);
}

@end

@implementation TCNull

+ (instancetype)null
{
	static TCNull* null = nil;
	if (null == nil)
	{
		null = [[self alloc] init];
	}
	return null;
}

- (void)doesNotRecognizeSelector:(SEL)aSelector
{
	raise(SIGINT);
}

@end