What are the common use cases for __IPHONE_OS_VERSION_MAX_ALLOWED?

Question

What are the situations in which you would use the __IPHONE_OS_VERSION_MAX_ALLOWED check? What about __IPHONE_OS_VERSION_MIN_REQUIRED?

Answer 1

a practical implementation/example of using instancesRespondToSelector:, expanding on @Nick Lockwood's anwser:

+(BOOL) testIsHeaderInConnectData:(NSData *) connectData {
    static NSString *headString = nil;
    static NSData *headData = nil;
    static BOOL rangeCheckOk = NO;
    static BOOL rangeCheckTestComplete = NO;
    if (!rangeCheckTestComplete) {
        rangeCheckOk = [NSData instancesRespondToSelector:@selector(rangeOfData:options:range:)]; 
        headString = @"HEAD ";
        headData = (rangeCheckOk?[[NSData alloc] initWithBytes:headString.UTF8String length:headString.length]:nil);
        headString = (rangeCheckOk?nil:[[NSString alloc ]initWithString:headString]);
        rangeCheckTestComplete = YES;
    }

    NSInteger testLength = connectData.length;
    BOOL isHeader = testLength > 5;
    if (isHeader) {
        testLength = (testLength < 128?testLength:128);
        if (rangeCheckOk) {
             isHeader = [connectData rangeOfData:headData options:0 range:(NSRange){0,testLength}].location!=NSNotFound;
        } else {
            NSString *headStart = [[NSString alloc] initWithBytes:connectData.bytes length:testLength encoding:NSUTF8StringEncoding];
            isHeader = [headStart rangeOfString:headString].location!=NSNotFound;
            [headStart release];
        }
    }
    return isHeader;
}