private synchronized T evaluate() {
		if (!_evaluated) {
			_value = _supplier.get();
			_evaluated = true;
		}

		return _value;
	}
If a value is evaluated, performs the given action with the value,
otherwise does nothing.

@since 8.1

@param action the action to be performed if a value is evaluated
jenetics/src/main/java/io/jenetics/internal/util/Lazy.java