What's the Point of (NSError**)error?

Question

Example: The -save: method of NSManagedObjectContext is declared like this:

- (BOOL)save:(NSError **)error

Since

Answer 1

It is what some people refer to as an "out" parameter.

You're not passing a pointer to an NSError object, you're passing a pointer to a local variable. This gives the called method the ability to modify your local variable; in this case, to assign it to an NSError instance.

Perhaps what's confusing is that the local variable you're passing to save: is itself a pointer, so the variable type ends up being a pointer to a pointer.

Bottom line, it's a pointer to a local variable, and it works the same whether the local variable is an int or an NSError*.