¿Cuándo se liberan estos objetos bajo ARC?

Tengo algunas preguntas sobre ARC (conteo automático de referencias):

CFURLRef url = (__bridge CFURLRef)[NSURL fileURLWithPath:appPath];
//Question 1: Here, I would expect the NSURL object to be autoreleased and
//therefore the CFURLRef will also be available for “a while.” Is this correct?

url = NULL;
//Question 2: Will this cause the NSURL to be released immediately?
NSURL *url = [NSURL fileURLWithPath:appPath];
url = nil;
//Question 3: Does the “url = nil” result in an immediate release of the NSURL?
NSURL *url = [[NSURL alloc] initWithString:@"/something"];
url = nil;
//Question 4: What about this?

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