objective c - Why compiler doesn't return error on [NSObject init] -


when try compile following code:

int main(int argc, const char * argv[]) {     @autoreleasepool {         [nsobject init];     }     return 0; }

compiler let build , app crashes in runtime following exception:

2017-08-14 14:56:07.937859-0700 nsobjectinit[30512:11241814] *** terminating app due uncaught exception 'nsinvalidargumentexception', reason: '*** +[nsobject<0x7fff9fd83140> init]: cannot init class object.' *** first throw call stack: (     0   corefoundation                      0x00007fff818e32cb __exceptionpreprocess + 171     1   libobjc.a.dylib                     0x00007fff966f348d objc_exception_throw + 48     2   corefoundation                      0x00007fff8196517f +[nsobject(nsobject) init] + 127     3   nsobjectinit                        0x0000000100000f2d main + 61     4   libdyld.dylib                       0x00007fff96fd9235 start + 1     5   ???                                 0x0000000000000001 0x0 + 1 ) libc++abi.dylib: terminating uncaught exception of type nsexception

as understand, there +init method in nsobject class, didn't find in public headers , if private, complier should tell there no such method. ideas why compiler let build code?

classes objects. there implicit "meta-class" each class , class 1 , instance of meta-class. think of "class method on class foo" instance method on class meta-foo.

in further quirk, meta-class of root class of class hierarchy subclass of root class itself. meta-nsobject inherits nsobject. class nsobject instance of itself!

so, instance method of nsobject class method of nsobject. is, can invoked on nsobject class itself. that's why compiler doesn't have problem [nsobject init].

http://sealiesoftware.com/blog/archive/2009/04/14/objc_explain_classes_and_metaclasses.html


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