Re: !foo vs foo == nil
Re: !foo vs foo == nil
- Subject: Re: !foo vs foo == nil
- From: "Michael Ash" <email@hidden>
- Date: Wed, 20 Aug 2008 23:03:10 -0400
On Wed, Aug 20, 2008 at 7:56 PM, John C. Randolph <email@hidden> wrote:
>
> On Aug 20, 2008, at 4:15 PM, Torsten Curdt wrote:
>>
>> There was a common perception that NULL is not really the same as nil. But
>> seems like in the end it really is (void*)0.
>
> They differ in type, not in value.
>
> "NULL" is (void *) 0.
> "nil" is (id) 0.
> "Nil" is (Class) 0.
This is true conceptually but not as far as their actual definition.
NULL can be either 0 or (void *)0. Nil and nil don't have a formal
definition, as Objective-C lacks a formal specification, but on my
machine they are both defined to be either 0 in 32-bit or (0L) in
64-bit. But for maximal clarity you should use them as you specify
above.
> Personally, I prefer "if (!foo)" over "if (foo == nil)", because the latter
> has the hazard of a typo that compiles. You can lose a fair bit of time
> staring at "if (foo = nil)" before you spot the mistake.
This hazard goes away if you turn on the appropriate warnings. I
compile all of my code with "-W -Wall -Wno-unused-parameter", and it
has caught much more than just this error over the years.
Mike
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