NSMutable class declares the programmatic interface to objects that manage mutable associations of keys and values. It adds modification operations to the basic operations it inherits from
Setting Values Using Subscripting
In addition to the provided instance methods, such as
set, you can access
NSDictionary values by their keys using subscripting.
There should typically be little need to subclass
NSMutable. If you do need to customize behavior, it is often better to consider composition rather than subclassing.