gistfile1.m

//
//  main.m
//  nil
//
//  Created by Ullrich Schäfer on 13.05.14.
//  Copyright (c) 2014 nxtbgthng GmbH. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface Object : NSObject
@property id property;
@end

@implementation Object @end

int main(int argc, const char * argv[])
{

    @autoreleasepool {
        Object *o1 = [Object new];
        Object *o2 = [Object new];
        Object *o3 = [Object new];
        o2.property = @"2";
        NSArray *array = @[o1, o2, o3];
        
        NSArray *result = [array valueForKey:@"property"];
        
        NSLog(@"Result: %@", result);
        
    }
    return 0;
}

Output:

Result: (
    "<null>",
    2,
    "<null>"
)