main.cc

#include <stdio.h>

struct Basest {
  virtual void foo() {
    return this->bar();
  }

  virtual void bar() = 0;
};

struct Mother: virtual Basest {
  virtual void bar() override {
    puts("Mother");
  }
};

struct Father: virtual Basest {
  virtual void foo() override {
    puts("Father");
    this->bar();
  }
};

struct Derivest
    : virtual Mother
    , virtual Father {};

int main() {
  Basest *p = new Derivest;
  p->foo();
}