NSString category to validate contents as an email address

gistfile1.m

@interface NSString (CLUEmailAdditions)
- (BOOL)isValidEmailAddress;
@end

@implementation NSString (CLUEmailAdditions)

static NSString* CLUEmailAddressPattern = @"^([0-9a-zA-Z]([-.\\w]*[0-9a-zA-Z])*@([0-9a-zA-Z][-\\w]*[0-9a-zA-Z]\\.)+[a-zA-Z]{2,9})$";

// NB - mostly yoinked from https://github.com/jPaolantonio/JPValidation/blob/master/JPValidators/JPValidatorEmail.m
- (BOOL)isValidEmailAddress {
    static NSRegularExpression* emailRegularExpression;
    if (!emailRegularExpression) {
        emailRegularExpression = [NSRegularExpression regularExpressionWithPattern:CLUEmailAddressPattern options:NSRegularExpressionCaseInsensitive error:nil];
    }
    // TODO - consider supporting comma separated addresses
    NSUInteger numberOfMatches = [emailRegularExpression numberOfMatchesInString:self options:0 range:NSMakeRange(0, self.length)];
    return numberOfMatches == 1;
}

@end