Way to create version proof code in ARC environment. (https://www.leapingbytes.com/blog/version_proofing_your_code_arc_twist)

NSString+LBToolbox.h

#import <Foundation/Foundation.h>

@interface NSString (LBToolbox)

- (CGSize) sizeWithWidth: (CGFloat) width andFont: (UIFont*) font;
@end

NSString+LBToolbox.m

#import "NSString+LBToolbox.h"


#ifdef __IPHONE_6_0
@interface NSString (HappyARC)
- (CGRect) boundingRectWithSize: (CGSize) size options: (NSStringDrawingOptions) options attributes: (id) attributes context: (id) context;
@end
#endif

@implementation NSString (LBToolbox)

- (CGSize) sizeWithWidth: (CGFloat) width andFont: (UIFont*) font {
    CGSize size = CGSizeMake( width, 2048);
    CGSize result;
    
    if ([self respondsToSelector:@selector(boundingRectWithSize:options:attributes:context:)]) {
        NSDictionary* attributes = [NSDictionary dictionaryWithObjectsAndKeys: font, NSFontAttributeName, nil];
        result = [self boundingRectWithSize: size options:NSStringDrawingUsesLineFragmentOrigin attributes:attributes context: nil].size;
    }
    else {
        result = [self sizeWithFont: font constrainedToSize: size];
    }
    result.width = width;
    
    return result;
}

@end