If subroutines is not existed but hex code will generated.
The PSoC work with no these subroutines.
You don't get an error because 'ConstCopy' is not actually used. An implicit declaration is not really a compiler error because most times the compiler can infer the method definition properly from its usage.
You will get an error about the undefined method from the linker. But since the linker doesn't need the 'ConstCopy' method, it doesn't complain. And this is because you don't call the 'DebugCommand' method, so it gets removed by the linker.
If you call the debug method, you will get an error as you expect.