Singleton objective c clarification

Question

as I continue my studies the book implemented a singleton. I understood the reason why use it but I just wanted some clarification regarding the code.

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Answer 1

For function-static variables the line

static BNRItemStore *defaultStore = nil;

is not an assignment. Rather, it is static initialization, which happens only once - the first time the code goes through your function. In subsequent invocations the value will not be nil, because you assign a non-nil value to it.

Your implementation is safe in single-threaded environments. For concurrent environments you would need to add some form of synchronization.