Understanding copy in the Objective-c

Whether an instance object in Objective-c supports a copy operation depends on whether the object implements the Nscopying protocol:

@protocol nscopying-(ID) Copywithzone: (Nszone *) zone; @end

For mutablecopy operations, there is a nsmutablecopying protocol:

@protocol nsmutablecopying-(ID) Mutablecopywithzone: (Nszone *) zone; @end

We see that there are copy and Mutablecopy methods in the NSObject interface, is it wrong to say that we must follow the agreement above?

@interface NSObject <NSObject> {    Class isa  objc_isa_availability;} ........ -(ID) copy; -(ID) mutablecopy; ....... @end

Let's do a test:

    // test nsobject copy    NSObject *originobject = [[NSObject alloc] init];     *copiedobject = [originobject copy];     *mutablecopiedobject = [Originobject mutablecopy];    NSLog (@ "%@,%@,%@", Originobject, Copiedobject, Mutablecopiedobject);

When the code executes to [originobject copy] crash, it is suggested that NSObject does not implement the Nscopying protocol method,

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Understanding copy in the Objective-c