Array operation doesn't check array bounds

[simendsjo]

        int[] a = [1,2,3];

        int[4] b;
        assert(b == [0,0,0,0]);
        b = a[] * 3; // oops... a[] * 3 takes element outside a's bounds
        assert(b[$-1] == 0); // fails.. last element is *(a.ptr+3) * 3