class method where self if used within a block

Question

I've got a class method that uses `dispatch_once` to create a static object. Inside the `dispatch_once` block I use `[self class]` and was wondering if I need to use a weak reference to `self` to avoid a retain cycle? ``` + (NSArray *)accountNames{ static NSArray *names = nil; static dispatch_once_t predicate; dispatch_once(&predicate, ^{ names = [[[self class] accounts] allKeys]; names = [names sortedArrayUsingSelector:@selector(caseInsensitiveCompare:)]; }); return names; } ``` If I use a weak reference to `self` I get a warning: ``` + (NSArray *)accountNames{ static NSArray *names = nil; static dispatch_once_t predicate; __weak TUAccount *wself = self; dispatch_once(&predicate, ^{ names = [[[wself class] accounts] allKeys]; names = [names sortedArrayUsingSelector:@selector(caseInsensitiveCompare:)]; }); return names; } ``` Incompatible pointer types initializing 'TUAccount *__weak' with an expression of type 'const Class' Because I get a warning I don't think I need to use a weak r…

Accepted Answer

There is no reason to worry about a retain cycle here, because it's meaningless to retain or release a class object -- retain and release simply have no effect.

Your attempt at making a weak reference is wrong, because you are taking a class object `self` and trying to cast it to an instance of `TUAccount`. The two are completely different things.

Also, you can simplify:

```
names = [[[self class] accounts] allKeys];
```

Since self is already a class, [self class] == self, so do this instead:

```
names = [[self accounts] allKeys];
```

class method where self if used within a block

Solution

Problem