main.m

#import <Foundation/Foundation.h>

// clang -o main -framework Foundation main.m

int main(int argc, const char*argv[]) {
  @autoreleasepool {
    NSLog(@"%@", (@42).class); // __NSCFNumber
    NSLog(@"%@", (@YES).class); // __NSCFBoolean
    NSLog(@"%@", @"Hello".class); // __NSCFConstantString
    NSLog(@"%@", [NSString stringWithFormat:@"%d", 42].class); // NSTaggedPointerString
    NSLog(@"%@", [NSData dataWithBytes:"ABC" length:3].class); // _NSInlineData
    NSLog(@"%@", [@"ABC" dataUsingEncoding:NSUTF8StringEncoding].class); // NSConcreteMutableData
    NSLog(@"%@", @[@42].class); // __NSSingleObjectArrayI
    NSLog(@"%@", @[@42, @43].class); // __NSArrayI
    NSLog(@"%@", [NSArray array].class); // __NSArray0
    return 0;
  }
}