[MESOS-2756] Update style guide: Avoid object slicing

• Type: Improvement
• Status: Accepted
• Priority: Major
• Resolution: Unresolved
• Labels: c++ mesosphere
• Story Points: 1
• Assignee: Joris Van Remoortere
• Reporter: Joris Van Remoortere
• Shepherd: Benjamin Hindman
• Created: 20/May/15 23:43
• Updated: 26/Nov/18 13:36

Description

In order to improve the safety of our code base, let's augment the style guide to:
"Disallow public construction of base classes"
so that we can avoid the object slicing problem. This is a good pattern to follow in general as it prevents subtle semantic bugs like the following:

ObjectSlicing.cpp

#include <stdio.h>
#include <vector>

class Base {
  public:
  Base(int _v) : v(_v) {}
  virtual int get() const { return v; }
  protected:
  int v;
};

class Derived : public Base {
  public:
  Derived(int _v) : Base(_v) {}
  virtual int get() const { return v + 1; }
};

int main() {
  Base b(5);
  Derived d(5);
  std::vector<Base> vec;
  vec.push_back(b);
  vec.push_back(d);
  for (const auto& v : vec) {
    printf("[%d]\n", v.get());
  }
}