Serializing dictionary to NSObjects, a la Go's json package

POD.h

#import <Foundation/Foundation.h>

@interface POD : NSObject<NSCopying>

-(nonnull NSString *)description;
-(nonnull NSDictionary *)toDictionary;
+(nonnull id)fromDictionary:(nonnull NSDictionary *)dict;
-(nonnull id)copyWithZone:(nullable NSZone *)zone;

@end

POD.m

#import "POD.h"
#import "objc/runtime.h"

@implementation POD

-(NSString *)description {
    return [[[self class] description] stringByAppendingString:[[self toDictionary] description]];
}

-(NSDictionary *)toDictionary {
    NSMutableDictionary *d = [NSMutableDictionary dictionary];
    unsigned int outCount, i;
    objc_property_t *properties = class_copyPropertyList([self class], &outCount);
    for(i = 0; i < outCount; i++) {
        objc_property_t property = properties[i];
        const char *propName = property_getName(property);
        if (!propName)
            continue;
        NSString *key = [NSString stringWithUTF8String:propName];
        if ([self valueForKey:key] == nil)
            continue;
        [d setObject:[POD clone:[self valueForKey:key]] forKey:key];
    }
    free(properties);
    return d;
}

+(NSArray<NSString *> *)typeMethodToType:(NSString *)name {
    static NSRegularExpression *regex;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        regex = [NSRegularExpression
                 regularExpressionWithPattern:@"_T_(.*)_T_(.*)"
                 options:0
                 error:nil];
    });
    NSTextCheckingResult *r = [regex firstMatchInString:name options:0 range:NSMakeRange(0, [name length])];
    if (!r)
        return nil;
    return @[[name substringWithRange:[r rangeAtIndex:1]],
             [name substringWithRange:[r rangeAtIndex:2]]];
}

+(NSDictionary<NSString *, NSString *> *)typeMethods {
    unsigned int methodCount = 0;
    const char *cls = [NSStringFromClass([self class]) cStringUsingEncoding:NSUTF8StringEncoding];
    Method *methods = class_copyMethodList(objc_getMetaClass(cls), &methodCount);
    NSMutableDictionary *rv = [NSMutableDictionary dictionary];
    
    for (unsigned int i = 0; i < methodCount; i++) {
        Method method = methods[i];
        NSString *name = [NSString stringWithUTF8String:sel_getName(method_getName(method))];
        NSArray<NSString *> *methodAndType = [self typeMethodToType:name];
        if (methodAndType)
            rv[methodAndType[0]] = methodAndType[1];
    }
    
    free(methods);
    return rv;
}

+(id)fromDictionary:(NSDictionary *)dict {
    unsigned int outCount, i;
    POD *obj = [[[self class] alloc] init];
    
    objc_property_t *properties = class_copyPropertyList([self class], &outCount);
    NSDictionary<NSString *, NSString *> *types = [self typeMethods];
    
    for(i = 0; i < outCount; i++) {
        objc_property_t property = properties[i];
        const char *propName = property_getName(property);
        const char *propAttr = property_getAttributes(property);
        if (!propName || !propAttr)
            continue;
        if (strncmp(propAttr, "T@\"", 3) != 0)
            continue;
        propAttr = propAttr+3;
        char *end = strchr(propAttr, '"');
        NSString *key = [NSString stringWithUTF8String:propName];
        NSString *type = [[NSString alloc] initWithBytes:propAttr length:(end-propAttr) encoding:NSUTF8StringEncoding];
        
        NSObject *value;
        Class typeClass = NSClassFromString(type);
        if ([type isEqualToString:@"NSArray"]) {
            NSString *inner = types[key];
            if (!inner)
                @throw [NSException exceptionWithName:@"IllegalState"
                                               reason:[NSString stringWithFormat:@"cannot find inner type of type %@", key]
                                             userInfo:nil];
            NSMutableArray *ar = [NSMutableArray arrayWithCapacity:[dict[key] count]];
            Class cls = NSClassFromString(inner);
            for (id obj in dict[key]) {
                if ([cls isSubclassOfClass:[POD class]])
                    [ar addObject:[cls fromDictionary:obj]];
                else
                    [ar addObject:obj];
            }
            value = ar;
        } else if ([typeClass isSubclassOfClass: [POD class]])
            value = [typeClass fromDictionary:dict[key]];
        else
            value = dict[key];
        
        [obj setValue:value forKey:key];
    }
    free(properties);
    return obj;
    
}

+(id)clone:(id)x {
    if ([x isKindOfClass:[POD class]])
        return [x toDictionary];
    if ([x isKindOfClass:[NSArray class]])
        return [POD clonePODArray:x];
    if ([x isKindOfClass:[NSDictionary class]])
        return [POD clonePODDictionary:x];
    return x;
}

+(NSDictionary *)clonePODDictionary:(NSDictionary *)dict {
    NSMutableDictionary *d = [NSMutableDictionary dictionaryWithDictionary:dict];
    for (id key in d) {
        id val = d[key];
        if ([val isKindOfClass:[POD class]]) {
            d[key] = [val toDictionary];
        }
    }
    return d;
}

+(NSArray *)clonePODArray:(NSArray *)ar {
    NSMutableArray *a = [NSMutableArray arrayWithArray:ar];
    for (int i=0; i<[a count]; i++) {
        id val = a[i];
        if ([val isKindOfClass:[POD class]]) {
            a[i] = [val toDictionary];
        }
    }
    return a;
}

- (id)copyWithZone:(nullable NSZone *)zone {
    NSObject *clone = [[[self class] alloc] init];
    [clone setValuesForKeysWithDictionary:[self toDictionary]];
    return clone;
}

@end