Method to do case insensitive string comparisons, working around the method returning `YES` if the receiver is `nil`.

NSString+Equality.h

#import <Foundation/Foundation.h>

/** Methods to help with determining string equality */
@interface NSString (Equality)

/**
 * Returns `YES` if the receiving string is equal to the
 * argument, ignoring case.
 *
 * So `latex` will be equal to `LaTeX` for instance.
 *
 * @param string The string to compare with
 * @return `YES` if the strings are equal. `NO` otherwise.
 */
- (BOOL)isEqualIgnoringCase:(NSString *)string;

@end

NSString+Equality.m

#import "NSString+Equality.h"

@implementation NSString (Equality)

- (BOOL)isEqualIgnoringCase:(NSString *)string {
    return [self caseInsensitiveCompare:string] == NSOrderedSame;
}

@end