private Evaluator<G, C> __evaluator() {
			return _evaluator instanceof FitnessEvaluator<G, C> fe
				? new FitnessEvaluator<>(fe.function(), fitnessExecutor())
				: _evaluator;
		}
Builds a new {@code Engine} instance from the set properties.

@return a new {@code Engine} instance from the set properties
jenetics/src/main/java/io/jenetics/engine/Engine.java