Internal error when use mapped class of double[] on iOS

IDE: VS 2015
Version: 8.4.96.2033
Target (If relevant): iOS
Description:

I’ve used double[] as vector to perform some animation arithmetic, and then I realize I can use mapped type feature to override operators of double[].

Then here’s a problem on iOS:

public __mapped class DoubleVector => double[] {

    public static DoubleVector operator-(DoubleVector a) {
        // test code
        return a;
    }
}

public class TestClass {
    public static void test() {
        DoubleVector a = new double[] { 1,2 };

        // (E0) Internal error: Object reference not set to an instance of an object.
        DoubleVector b = -a;
    }
}

Thanks, logged as bugs://75995

bugs://75995 got closed with status fixed.

Logged as bugs://i63929.

bugs://i63929 was closed as fixed.