NSString category containing an Objective-C port of @henrik's slugalize helper method: https://github.com/henrik/slugalizer?source=c

NSString+RAInflections.h

//
// Created by Robert Audi on 07/04/13.
// Updated on 08/21/14
//

#import <Foundation/Foundation.h>

@interface NSString (RAInflections)

- (NSString *)slugalize;

@end

NSString+RAInflections.m

//
// Created by Robert Audi on 07/04/13.
// Updated on 08/21/14
//

#import "NSString+RAInflections.h"

@implementation NSString (RAInflections)

/**
 * Port of the slugalized helper created by @henrik
 * https://github.com/RobertAudi/slugalizer
 */
- (NSString *)slugalize
{
    NSString        *separator        = @"-";
    NSMutableString *slugalizedString = [NSMutableString string];
    NSRange         replaceRange      = NSMakeRange(0, self.length);

    // Remove all non ASCII characters
    NSError *nonASCIICharsRegexError = nil;
    NSRegularExpression *nonASCIICharsRegex = [NSRegularExpression regularExpressionWithPattern:@"[^\\x00-\\x7F]+"
                                                                                        options:0
                                                                                          error:&nonASCIICharsRegexError];
    slugalizedString = [[nonASCIICharsRegex stringByReplacingMatchesInString:self
                                                                     options:0
                                                                       range:replaceRange
                                                                withTemplate:@""] mutableCopy];

    // Turn non-slug characters into separators
    NSError *nonSlugCharactersError = nil;
    NSRegularExpression *nonSlugCharactersRegex = [NSRegularExpression regularExpressionWithPattern:@"[^a-z0-9\\-_\\+]+"
                                                                                            options:NSRegularExpressionCaseInsensitive
                                                                                              error:&nonSlugCharactersError];
    slugalizedString = [[nonSlugCharactersRegex stringByReplacingMatchesInString:slugalizedString
                                                                         options:0
                                                                           range:replaceRange
                                                                    withTemplate:separator] mutableCopy];

    // No more than one of the separator in a row
    NSError *repeatingSeparatorsError = nil;
    NSRegularExpression *repeatingSeparatorsRegex = [NSRegularExpression regularExpressionWithPattern:[NSString stringWithFormat:@"%@{2,}", separator]
                                                                                              options:0
                                                                                                error:&repeatingSeparatorsError];

    slugalizedString = [[repeatingSeparatorsRegex stringByReplacingMatchesInString:slugalizedString
                                                                           options:0
                                                                             range:replaceRange
                                                                      withTemplate:separator] mutableCopy];

    // Remove leading/trailing separator
    slugalizedString = [[slugalizedString stringByTrimmingCharactersInSet:[NSCharacterSet characterSetWithCharactersInString:separator]] mutableCopy];

    return [slugalizedString lowercaseString];
}

@end

"// Remove leading/trailing separator" should use variable separator
slugalizedString = [[slugalizedString stringByTrimmingCharactersInSet:[NSCharacterSet characterSetWithCharactersInString:separator]] mutableCopy];

Also, options:nil -> options:0

@davidlawson Updated! Thanks 👍

The replaceRange in line 37 should be recalculated, as slugalizedString may be shorter than the original string. If the original string ends in a non-ascii character, it crashes at line 35

Hi thanks for this. I fixed the range issue in my fork if you would like to update.

Should do
replaceRange = NSMakeRange(0, slugalizedString.length);
after all stringByReplacingMatchesInString