Re: Strange compile error when g++ work with std=c++20.

[Jonathan Wakely via Gcc-bugs]

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However, Andrew already explained why GCC is correct and this is not a
GCC bug. Just use DECLARE_SINGLETON(ReceiverManager) to fix your code.
The constructor should be declared as ReceiverManager() just like your
destructor is declared as ~ReceiverManager(), not as
~ReceiverManager<MessageT>().