void ICommandPatternObserver.OnCommandSpecified(ICommandSpec spec) => Specified?.Invoke((TSpec)spec);
void ICommandPatternObserver <TSpec> .OnCommandSpecified(TSpec spec) => Specified?.Invoke(spec);
void ICommandPatternObserver.OnCommandSpecified(ICommandSpec spec) => Specified?.Invoke((TSpec)spec);
void ICommandPatternObserver <TSpec> .OnCommandSpecified(TSpec spec) => Specified?.Invoke(spec);