Open Radar

 
Summary:
An NSTaggedPointerString of an empty value can be created in some circumstances. When setting the title property of a UIBarButtonItem to it, it interprets it as nil. However, for other types of strings it behaves properly

Steps to Reproduce:
Create an XCTestCase that looks like this.

One test will fail. One won't.

//
//  TitleExampleTests.m
//  TitleExampleTests
//
//  Created by Mike Lewis on 9/23/15.
//  Copyright © 2015 Square, Inc. All rights reserved.
//

#import <XCTest/XCTest.h>
#import <objc/runtime.h>

static NSString *const EmptyString = @"";

@interface TitleExampleTests : XCTestCase

@property (nonatomic) UIViewController *viewController;

@end


@implementation TitleExampleTests

- (void)setUp {
    [super setUp];
    self.viewController = [[UIViewController alloc] init];
    self.viewController.navigationItem.backBarButtonItem = [[UIBarButtonItem alloc] init];
}

// This case will fail.
- (void)testTaggedPointer {
    // It's a bit tricky to make a tagged pointer of an empty string, but this will do it.
    NSString *empty = [[[@"\"\"" mutableCopy] copy] substringWithRange:NSMakeRange(1, 0)];
    
    NSAssert([@"NSTaggedPointerString" isEqualToString:NSStringFromClass([empty class])], @"Expecting this to equal a tagged pointer string");
    XCTAssertEqualObjects(empty, @"");
    
    self.viewController.navigationItem.backBarButtonItem.title = empty;
    
    // This will fail in iOS 9
    XCTAssertNotNil(self.viewController.navigationItem.backBarButtonItem.title);
}

// This case will pass
- (void)testConstant {
    NSAssert(![@"NSTaggedPointerString" isEqualToString:NSStringFromClass(EmptyString.class)], @"Expecting this to not be a tagged pointer string");
    self.viewController.navigationItem.backBarButtonItem.title = EmptyString;
    XCTAssertNotNil(self.viewController.navigationItem.backBarButtonItem.title);
}

@end


Expected Results:
It should be empty string in both cases

Actual Results:
It isn't an empty string, but rather nil in the case of a tagged pointer.

Version:
xcode 7, iOS 9.0 simulator/device

Notes:
Not sure if the substringWithRange should ever return a tagged pointer of an empty string. It was actually very difficult reproducing a tagged empty string to be created.

Configuration:
When running tests, when in the playground. Whenever

Attachments: