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I want to ask a question about the objective C. When I study the library from the apple developer website. I always see that there are some subclass called "mutable". For example, the NSArray and NSMutableArray. What does it mean about this word. Are there some special meaning? Can anyone tell me? Thank you.
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Overview. The NSMutableArray class declares the programmatic interface to objects that manage a modifiable array of objects. This class adds insertion and deletion operations to the basic array-handling behavior inherited from NSArray .
A mutable object is an object whose state can be modified after it is created. Immutables are the objects whose state cannot be changed once the object is created. Strings and Numbers are Immutable.
Mutable and immutable are English words meaning "can change" and "cannot change" respectively. The meaning of the words is the same in the IT context; i.e. a mutable string can be changed, and. an immutable string cannot be changed.
Mutable data types are those whose values can be changed or new values can be assigned to them. List, Sets, and Dictionary in Python are examples of some mutable data types in Python. Immutable data types are those, whose values cannot be modified once they are created.
In object-oriented and functional programming, an immutable object (unchangeable object) is an object whose state cannot be modified after it is created.
You need mutable classes to deal with situations when transforming a class from state A to state Z would produce a lot of intermediate objects, which you would rather not spend time creating. One classic example is concatenating an array of strings.
It means you can change its values. If you look at the NSMutableArray docs, you'll see it defines extra methods like -addObject:. NSArray by itself doesn't have these (and can thus be more efficient / take less memory in implementation).
Also note, if you call [myMutableArray copy] you'll get a non-mutable copy of it (which you must later release0. And similarly there's -mutableCopy.
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Mutable means you can change it. Look at the difference between addObject in NSMutableArray and arrayByAddingObject in NSArray.
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