hello, this is some code in MyTest.h file. I import MyTest.h into ViewController.m , then get some error. duplicate symbol '_MyTestType' in: ...ViewController.o ... MyObjTest.o . /// Can't run, but OK Xcode15, Why ??? //NSString * const MyTestType = @"MyTestType"; /// OK static NSString * const MyTestType = @"MyTestType";