Query for below code of ASIHTTPRequest

what is purpose of using ^ sign in below code?

__block ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:sourceURL];
    [request setCompletionBlock:^{
        NSLog(@"Image downloaded.");
        NSData *data = [request responseData];
        image = [[UIImage alloc] initWithData:data];
        [[NSNotificationCenter defaultCenter] postNotificationName:@"com.razeware.imagegrabber.imageupdated" object:se开发者_开发问答lf];
    }];
    [request setFailedBlock:^{
        NSError *error = [request error];
        NSLog(@"Error downloading image: %@", error.localizedDescription);
    }];

The caret (^) introduces a block literal and the curly braces enclose statements that make up the body of the block. You can think of a block as being similar to an anonymous function.

You should refer this article..

^ Sign symbolizes the block of code as the whole function is written der itself rather than creating a method and calling it using a @selector.

Hope this helps you.