Re: Objective-C variadic methods vs. NSArray et al.
Re: Objective-C variadic methods vs. NSArray et al.
- Subject: Re: Objective-C variadic methods vs. NSArray et al.
- From: "Clark Cox" <email@hidden>
- Date: Fri, 21 Nov 2008 15:52:44 -0800
On Fri, Nov 21, 2008 at 3:40 PM, Scott Thompson <email@hidden> wrote:
> Technical QA 1405 concerns the creation of Objective-C methods that take
> variable number of arguments... so called variadic methods. Happily the
> mechanisms just use the standard C mechanisms (va_start and friends).
>
> That being the case, why is it that methods like arrayWithObjects: require
> you to nil terminate the list of arguments? Is it simply tradition, or some
> kind of optimization?
Without the nil, how would the method know when to stop fetching
arguments with va_arg? This is true in C too, you have to have some
way that tells you how many parameters are being passed and what types
they are, and there are generally only two ways to do this:
1) Have the information encoded in the first parameter (like a printf
format string)
2) Have some sentinel value marking the end of the list (like the nil
passed to arrayWithObjects:)
--
Clark S. Cox III
email@hidden
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