dictionaryWithDictionary

dictionaryWithDictionary is a class method of NSDictionary that creates and returns a new dictionary containing the entries of a given dictionary. The resulting dictionary is immutable and holds the same key-value pairs as the input. The method performs a shallow copy: the keys and values themselves are not copied, only the dictionary structure, and the objects referenced by those keys and values are reused.

The method signature is + (NSDictionary *)dictionaryWithDictionary:(NSDictionary *)dictionary;. It serves as a convenience constructor, equivalent to alloc/initWithDictionary:, but typically returns an autoreleased object under manual reference counting. With ARC, memory management is handled automatically.

If the input dictionary is mutable, the new dictionary remains immutable. Passing nil to the method will usually raise an exception in Objective-C.

Common usage includes producing an immutable copy from a mutable dictionary or cloning an existing dictionary in a concise form. Example: NSDictionary *src = @{@"a": @1, @"b": @2}; NSDictionary *copy = [NSDictionary dictionaryWithDictionary:src];

Alternative initializers include -initWithDictionary:, and other copy operations such as -copy or -mutableCopy, depending on whether a mutable or immutable result is desired. dictionaryWithDictionary: is primarily used for straightforward, explicit creation of an immutable dictionary from an existing dictionary without manually allocating and initializing a new instance.

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