Mutable vs immutable object for instance variable in objective C

I have a class with a property sampleNames. It is of type NSSet. The instance variable I plan to use will be NSMutableSet.

the only reason I have for using NSMutableSet is convenience for myself. But I recall being 'told' that Mutable class should be used as sparingly as possible for some reason I cannot remember. I understand how to use both ways, so this si not so much a question about that.

What are the practical considerations when deciding whether or not to use a mutable class internally?

Please note, I am not at all interested in changing my PROPERTY to NSMutableSet. But the fact that I am using a different type internally made me think about why and I have no real justification other than convenience, Which I have found to be a bad justification by itself. Maybe it is the only reason, but i am not actively aware of what I am trading for the convenie开发者_开发百科nce.)

I think you are confused.

You use NSMutableSet when you need to change the contents of the set. You can only do that if it is mutable.

If you use NSSet, then you can't change the contents.

So ... your property declaration and your instance variable should be the SAME class. Either use NSSet if you don't need to change the contents or NSMutableSet if you do.

Having a different class for the property and the instance variable is a recipe for disaster ... it's not convenient and it is confusing = BAD ;-)