NSDictionary* json = (fetch from Internet) ...
User* user=[[User alloc] init];
user.userId =[json objectForKey:@"userId"];
user.nick= [json objectForKey:@"nick"];
user.image = [json objectForKey:@"image"];
user.age = [json objectForKey:@"age"];
...

NSError* err = nil;
User* user = [[User alloc] initWithDictionary:json error:&err];

···

//inspects the class,get's a list of the class properties
-(void)__inspectProperties
{
    //JMLog(@"Inspect class: %@",[self class]);
    
    NSMutableDictionary* propertyIndex = [NSMutableDictionary dictionary];
    
    //temp variables for the loops
    Class class = [self class];
    NSScanner* scanner = nil;
    NSString* propertyType = nil;
    
    // inspect inherited properties up to the JSONModel class
    while (class != [JSONModel class]) {
        //JMLog(@"inspecting: %@",NSStringFromClass(class));
        
        unsigned int propertyCount;
        objc_property_t *properties = class_copyPropertyList(class,&propertyCount);
        
        //loop over the class properties
        for (int i = 0; i < propertyCount; i++) {

            JSONModelClassProperty* p = [[JSONModelClassProperty alloc] init];

            //get property name
            objc_property_t property = properties[i];
            const char *propertyName = property_getName(property);
            p.name = [NSString stringWithUTF8String:propertyName];
            
            //JMLog(@"property: %@",p.name);
            
            //get property attributes
            char *attrs = property_getAttributes(property);
            NSString* propertyAttributes = [NSString stringWithUTF8String:attrs];
            
            if ([propertyAttributes hasPrefix:@"Tc,"]) {
                //mask BOOLs as structs so they can have custom convertors
                p.structName = @"BOOL";
            }
            
            scanner = [NSScanner scannerWithString: propertyAttributes];
            
            //JMLog(@"attr: %@",[NSString stringWithCString:attrs encoding:NSUTF8StringEncoding]);
            [scanner scanUpToString:@"T" intoString: nil];
            [scanner scanString:@"T" intoString:nil];

···

//finally store the property index in the static property index
objc_setAssociatedObject(self.class,&kClassPropertiesKey,[propertyIndex copy],OBJC_ASSOCIATION_RETAIN // This is atomic
                         );

//returns a list of the model's properties
-(NSArray*)__properties__
{
    //fetch the associated object
    NSDictionary* classProperties = objc_getAssociatedObject(if (classProperties) return [classProperties allValues];

    //if here,the class needs to inspect itself
    [self __setup__];
    
    //return the property list
    classProperties = objc_getAssociatedObject(return [classProperties allValues];
}