Re: Create an NSCharacterSet constant
Re: Create an NSCharacterSet constant
- Subject: Re: Create an NSCharacterSet constant
- From: Michael Ash <email@hidden>
- Date: Mon, 2 Nov 2009 11:20:14 -0500
On Mon, Nov 2, 2009 at 12:29 AM, Kyle Sluder <email@hidden> wrote:
> On Sun, Nov 1, 2009 at 9:19 PM, John Joyce
> <email@hidden> wrote:
>> Is it possible to create an NSCharacterSet constant?
>
> No. By definition, constants are assigned values at compile time.
> Objects other than strings can only be created at runtime. There is
> no way around this fact.
>
>> Is it best just to declare a global constant string, then initialize an
>> NSCharacterSet during app initialization? It certainly seems that is the
>> only real option.
>
> Answers will vary. You could use a static global variable which is
> assigned in +initialize, or you could use a static variable in a
> category on NSCharacterSet, or a number of other things. Basically
> what you really want is a singleton, not a constant.
>
> I'm partial to the following construct:
>
> + (Foo *)sharedFoo {
> static Foo *sharedFoo;
> dispatch_once_t once;
> dispatch_once(&once, ^{ sharedFoo = [[foo alloc] init]; }
> return sharedfoo;
> }
Watch out! The 'once' variable must be declared static as well.
Without it, if you're unlucky to get a zero-filled 'once' every time
through, this call will appear to work but leak a new Foo every time
you call it.
Mike
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