__bridge vs __bridge_transfer vs __bridge_retained

__bridge

Two way OBJECTIVE-C ← → CF

Transfers a pointer between Objective-C and Core Foundation with no transfer of ownership

-(void)greetViaBridge
{
    CFStringRef stringRef = CFStringCreateWithCString(NULL, "Hello World via bridge", kCFStringEncodingUTF8);
    NSString *text = (__bridge NSString *) stringRef;
    NSLog(@"%@", text);
    CFRelease(stringRef);
}

__bridge_transfer

CF → OBJECTIVE-C

Moves a Core Foundation pointer to Objective-C with transfer of the ownership to ARC

-(void)greetViaBridgeTransfer
{
    CFStringRef stringRef = CFStringCreateWithCString(NULL, "Hello World via bridge transfer", kCFStringEncodingUTF8);
    NSString *text = (__bridge_transfer NSString *) stringRef;
      
    NSLog(@"%@", text);
}

__bridge_retained

OBJECTIVE-C → CF

Moves an Objective-C pointer to Core Foundation and transfers ownership and also responsibility of releasing the memory to you

-(void)greetViaBridgeRetained
{
    NSString *text = @"Hello World via bridge retained";
    CFStringRef stringRef = (__bridge_retained CFStringRef)text;
    NSLog(@"NSString: %@", text);
    NSLog(@"CFStringRef: %@", stringRef);
    CFRelease(stringRef);
}