Example of "implicit ODR-use of a non-pure virtual member function that happens to be deleted"

Question

There is a sentence in the cppreference.com description of Deleted functions:

However, implicit ODR-use of a non-pure virtual member function that happens to be deleted is allowed.

Could you provide a code example of this case?

I tried to do this:

struct ff
{
    virtual int fd()
    {
        return 0;
    }
};
struct ddff : public ff
{
    int fd()
    {
        throw std::exception("ttt");
    }
};
struct dd : public ddff
{
      int fd() = delete;
};
int main()
{
    ff* d = new dd();
    d->fd();

But it brings a error:

Error C2282 'dd::fd' cannot override 'ddff::fd'

Answer 1

Thanks for comment:

Virtual functions are considered odr-used even if you never mentioned them in your code. What the sentence is saying is that such an odr-use is fine with deleted functions. Your error comes from the fact that deleted functions can't override non-deleted functions and vice versa.