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Why implement custom copy constructor in C++?
- In C++, copying is a very distinct operation that varies depending on the object that you deal with.
- If your class does not own any resource, consists only of trivially constructable types and does not encapsulate any logic, not implementing any custom constructors or destructor is actually a good practice.
- Copying becomes more complicated when your object becomes more complicated too, for instance, with classes holding pointers.
- To make a deep copy of the object, you must implement your custom copy constructor where you perform additional memory allocation dedicated for the copied object.
- Having std::make_shared only in a constructor allows you to control the dynamic memory allocation.
- When you put a non-copyable type inside your class and you don't implement a custom copy constructor, the compiler implicitly deletes the constructor of your class as well.
- Whenever you add a copy constructor to your class, you must add a default constructor as well.
- Another example is classes which are supposed to persist a cache specific for single class instance.
- Adding a custom copy constructor may become a fix for the autogenerated default copy constructor resulting in unexpected output
- Consider using std::weak_ptr if you need to implement a caching-like mechanism.
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