In Objective C, Usual implementation of singleton design pattern contains “static id theInstance = nil” in a method, why not outside?

Question

When i was going through Singleton design pattern in Objective C, I found lot of people using the below code to create it.

@interface Base : NSObject {} 

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Answer 1

static variables only get initialized once, regardless of if they're at global or local scope. In this case, you don't even need the nil - static storage class variables are zero-initialized by default. This declaration:

  static id theInstance;

is enough to be the same as what you have there.