Subclass NSCoder to encode to NSObject hierarchy (for debugging)

MyDebugCoder.m

@interface MyDebugCoder : NSCoder
+ (NSDictionary *)serializedJSONWithRootObject:(id<NSCoding, NSObject>)object;
@end

@implementation MyDebugCoder
{
    NSMutableDictionary *_jsonRoot;
    NSMutableArray *_values;
}

- (instancetype)init
{
    self = [super init];
    if (self) {
        _jsonRoot = [[NSMutableDictionary alloc] init];
        _values = [[NSMutableArray alloc] init];
        _jsonRoot[@"values"] = _values;
    }
    return self;
}

-(void)encodeValueOfObjCType:(const char *)type at:(const void *)addr
{
    switch(*type){
            // bool (C++)
        case 'B':
            [_values addObject:@(*(const bool *)addr)];
            break;
            // char
        case 'c':
        case 'C':
            [_values addObject:[NSString stringWithFormat:@"%c", *(const char *)addr]];
            break;
            // short
        case 's':
        case 'S':
            [_values addObject:@(*(const short *)addr)];
            break;
            // int
        case 'i':
        case 'I':
            [_values addObject:@(*(const int *)addr)];
            break;
            // long
        case 'l':
        case 'L':
            [_values addObject:@(*(const long *)addr)];
            break;
            // long long
        case 'q':
        case 'Q':
            [_values addObject:@(*(const long long *)addr)];
            break;
            // float
        case 'f':
            [_values addObject:@(*(const float *)addr)];
            break;
            // double
        case 'd':
            [_values addObject:@(*(const double *)addr)];
            break;

            // C-string (0 terminated)
        case '*':
            [_values addObject:@(*(const char**)addr)];
            break;


            // Obj-C object
        case '@':
            [self _appendObject:*(const id *)addr];
            break;

        case 'b': // bit-field "bNUMBITS"
        case 'v': // void
        case '[': // C-array
        case '#': // Class
        case ':': // selector
        case '{': // struct
        case '(': // union
        case '^': // pointer to TYPE "^TYPE"
        case '?': // unknown (including function pointers)
        default:
            // skip
            NSLog(@"skip %c", *type);
            break;
    }
}

-(void)encodeDataObject:(NSData *)data
{
    [self _appendObject:data];
}

-(NSInteger)versionForClassName:(NSString *)className
{
    Class objectClass = NSClassFromString(className);
    return objectClass ? [objectClass version] : NSNotFound;
}

+ (NSDictionary *)serializedJSONWithRootObject:(id<NSCoding, NSObject>)object
{
    TNLJSONCoder *coder = [[self alloc] init];
    [object encodeWithCoder:coder];
    [coder _addObjectDescription:object];
    return coder->_jsonRoot;
}

+ (id)_valueForObject:(id)object
{
    if (!object) {
        return [NSNull null];
    }

    if ([object isKindOfClass:[NSString class]] ||
        [object isKindOfClass:[NSNumber class]] ||
        [object isKindOfClass:[NSDate class]] ||
        [object isKindOfClass:[NSNull class]] ||
        [object isKindOfClass:[NSURL class]]) {
        return object;
    }
  
    if ([object isKindOfClass:[NSData class]]) {
        return [NSString stringWithFormat:@"<%@ %@, length=%tu>", NSStringFromClass([object class]), object, [(NSData *)object length]];
    }

    if ([object isKindOfClass:[NSDictionary class]]) {
        NSMutableDictionary *valueDictionary = [NSMutableDictionary dictionaryWithCapacity:[(NSDictionary *)object count]];
        [(NSDictionary *)object enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
            key = [self _valueForObject:key];
            obj = [self _valueForObject:obj];
            valueDictionary[key] = obj;
        }];
        return valueDictionary;
    }

    TNLJSONCoder *coder = [[[self class] alloc] init];
    [object encodeWithCoder:coder];
    [coder _addObjectDescription:object];
    return coder->_jsonRoot;
}

- (void)_appendObject:(const id)object
{
    [_values addObject:[[self class] _valueForObject:object]];
}

- (void)_addObjectDescription:(id<NSObject>)object
{
    NSString *description = [object description];
    if (![description hasPrefix:@"<"]) {
        description = [NSString stringWithFormat:@"<%@ %p>", NSStringFromClass([object class]), object];
    }
    _jsonRoot[@"object"] = description;
}

@end