> On Aug 12, 2016, at 9:16 AM, Steve Sisak <sgs-li...@codewell.com> wrote:
>
> There’s a standard idiom where immutable classes frequently have mutable
> subclasses (which expose the mutating methods).
>
> In this case, it’s common for the immutable (super)class to adopt NSCopying
> and the mutable subclass to also adopt NSMutableCopying.
>
> This way if you want to add an object to a collection, calling -copy has the
> effect of freezing the current value ― the immutable class can optimize this
> by just returning a new reference to the same object, but the caller doesn’t
> have to know whether the object was immutable or a mutable subclass.
Almost.
The design pattern for this is the class cluster.
Where the public interfaces may produce private subclasses that handle and
respond appropriately to the messages that make them one or the other.
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