Grand central dispatch - Aren39t static variables in an Objective-C class method shared across all subclasses

Questions

I m really perplexed. I have a class A with a class method that returns a shared cache instance:

+ (NSCache *)itemCache {
    static NSCache *itemCache;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        itemCache = [[NSCache alloc] init];
    });
    return itemCache;
}

I also have a subclass B of class A.

Whenever I call [A itemCache] I get one instance of the cache. Whenever I call [B itemCache] I get a different instance of the cache.

Are static variables unique to the particular class the method is called on? I thought they were shared across all subclasses.

  Edit    Nevermind, there was something else going. The world does indeed work like I thought it did. I have an app target and a test target. Class A was being included in both targets. Class B was only in the app target.

Answers

This code produces the expected behavior:

#import <Foundation/Foundation.h>

@interface A : NSObject
+ (NSCache *)itemCache;
@end

@implementation A
+ (NSCache *)itemCache {
    static NSCache *itemCache;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        itemCache = [[NSCache alloc] init];
    });
    return itemCache;
}

@end

@interface B : A
@end
@implementation B
@end


@interface C : A
@end
@implementation C
@end



int main(int argc, const char * argv[])
{

    @autoreleasepool {
            NSLog(@"%@ %@ %@", [A itemCache], [B itemCache], [C itemCache]);

    }
    return 0;
}

logs:

<NSCache: 0x1002000e0> <NSCache: 0x1002000e0> <NSCache: 0x1002000e0>

your issue must be else-where.

Source

License : cc by-sa 3.0

http://stackoverflow.com/questions/23087311/arent-static-variables-in-an-objective-c-class-method-shared-across-all-subclas

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