class Foo {
    Foo opBinary(string op)(ref Foo) {
        return null;
    }
}
void main() {
    auto f = new Foo;
    auto r1 = f * f;         // OK
    auto r2 = f * (new Foo); // Error.
}



DMD 2.064alpha gives:

test.d(9): Error: 'f' is not of arithmetic type, it is a test.Foo
test.d(9): Error: 'new Foo' is not of arithmetic type, it is a test.Foo


I think that's a bug. Even if that's not a bug, then I suggest to improve the error messages.