C++ Coding Standards: 101 Rules, Guidelines, and Best Practices

54. Avoid slicing. Consider Clone instead of copying in base classes

Summary

Sliced bread is good; sliced objects aren’t: Object slicing is automatic, invisible, and likely to bring wonderful polymorphic designs to a screeching halt. In base classes, consider disabling the copy constructor and copy assignment operator, and instead supplying a virtual Clone member function if clients need to make polymorphic (complete, deep) copies.

Discussion

When you build class hierarchies, usually the intent is to get polymorphic behavior. You want objects, once created, to preserve their type and identity. This goal conflicts with C++’s usual object copy semantics because the copy constructor is not virtual and cannot be made virtual. Consider:

The programmer’s ...