What is the difference between NSDictionary and NSMutableDictionary ?

Here is the difference between NSDictionary and NSMutableDictionary in Objective-C:

NSDictionary

• NSDictionary is an immutable collection of key-value pairs.
• The contents of an NSDictionary cannot be modified after it is created.
• Adding, removing or changing values in an NSDictionary will result in a compile-time error.
• NSDictionary is thread-safe and can be safely accessed from multiple threads.
• NSDictionary is optimized for fast lookup of values by key.

NSMutableDictionary

• NSMutableDictionary is a mutable subclass of NSDictionary.
• The contents of an NSMutableDictionary can be modified after it is created.
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