A programming question

I have used private inheritance. The base class public access members are still public access in the derived class. Therefore the derived class still can call the base class functions and access its public data. But the user who instantiates the derived class, cannot access the public member of the base class, hence private inheritance. Public inheritance is a "is-a" relationship. Private inheritance is a "implemented-in-terms-of" relationship. A useful example, is I like .NET string class and like a C++ string class with the same C# methods but I do not want to reimplement from scratch, so I derived from std::wstring with private inheritance to make use of its functionality, so that user of my string class cannot access the base class's std::wstring to avoid the confusion.

class MyString : private std::wstring
{
};

There is an excellent blog about this topic: [C++ Tutorial: Private Inheritance - 2020](https://www.bogotobogo.com/cplusplus/private\_inheritance.php)

David ONeil

(And also made me a bit sad, that we are overwriting the lives of other species to supposedly improve our own.)

The forgotten roots of science | C++ Programming | DWinLib

David ONeil

Thank you. Very helpful!

The forgotten roots of science | C++ Programming | DWinLib

Arthur V Ratz

Hi David, According to this, private inheritance in C++17 is primarily used whenever you're having a need to make all those public and protected members, in a base class, to become private in all derived descendant classes, and, thus not accessible via a derived class object. Whist, according to this, all public and protected members of a base class become protected in all derived classes. This is typically needed to make those public members of a base class to become protected in all descendent classes, rather than those methods are accessible via a derived class object.

Lost User

Yeah,

David O'Neil wrote:

we are overwriting the lives of other species to supposedly improve our own

One of my old coworkers has a wife that was working as a research scientist at the Tulane National Primate Research Center |[^] and she would describe some of her research. They have over 5,000 primates, you have absolutely no idea... what she was telling me was worse than anything you can possibly even imagine. Best Wishes, -David Delaune

Stefan_Lang

A good example, but most cases I've come across caring about these kind of problems use delegates instead of inheritance. Delegates come with the additional advantage to keep what would otherwise be the base class entirely out of the API (i. e. the headers). I. e. instead of putting this into your header:

class MyEncapsulatedBaseClass { // ...
public:
void doAwesomeStuff();
};
class MYAPI MyDerivedClass : private MyEncapsulatedBaseClass { // ...
public:
void doMoreAwsomeStuff(); // calls doAwesomeStuff() and more
};

you only put this in your header:

class MYAPI MyClass {
class MyEncapsulatedClass* delegate;
public:
void doMoreAwesomeStuff(); // uses delegate to do awesome stuff and then does more
};

The advantage of the latter is that you can switch to a different encapsulated class or change the function and data members in that class without affecting the API delivered to your clients. The only advantage of the former I can think of is, that with protected inheritance, that protection is not final, at least not for virtual member functions: another derived class can overide any protected virutal base function with a public one, making it accessible again! (Of course, if you want to retain that option, the question is why don't you use public inheritance to start with ? :wtf: )

GOTOs are a bit like wire coat hangers: they tend to breed in the darkness, such that where there once were few, eventually there are many, and the program's architecture collapses beneath them. (Fran Poretto)

Lost User

Yep, C++ has become such a feature-rich language. There are many tools in the programmers toolbox. Best Wishes, -David Delaune

W Balboos GHB

All one needs to do is recall images of live monkeys with the tops of their skulls removed and numerous wires implanted. There's a reason that there are groups who are outraged by these practices are sometimes even provoked to mass-releases by attacking the labs. Those who condemn them - maybe if they had a look first, before the lab covered up the less PR-improving experiments. Not just monkeys - much of animal testing is irrelevant. If we relied on its outcome, we'd consider aspiring toxic (cats) and chocolate toxic (dogs) - we'd make up for it with amanita phalloides as a tasty addition to our diet since it doesn't harm rabbits. That's a mushroom more commonly called "The Death Angel".

Ravings en masse^

"The difference between genius and stupidity is that genius has its limits." - Albert Einstein

"If you are searching for perfection in others, then you seek disappointment. If you seek perfection in yourself, then you will find failure." - Balboos HaGadol Mar 2010

Nemanja Trifunovic

One instance where I used private inheritance in pre C++ 11 days was to easily make a class non-copyable:

class fancy_type : private boost::noncopyable
{};

utf8-cpp

Lost User

W∴ Balboos, GHB wrote:

All one needs to do is recall images of live monkeys with the tops of their skulls removed and numerous wires implanted.

I don't know how you knew that, but she also told me that the experiments required that the primates were conscious to get accurate data. I don't know how she could sleep at night after doing something like that. It's disgusting. Best Wishes, -David Delaune

W Balboos GHB

Randor wrote:

I don't know how you knew that,

Pictures of that have been available for years (often showing up in donation requests from animal rights groups). Animals deliberately crippled, typically spinal cord damage, for experiments. Vivisection is common. Personally, I won't even wear leather as it's value-added to the slaughter-industry (and rather repulsive if you think about what it is).

Ravings en masse^

"The difference between genius and stupidity is that genius has its limits." - Albert Einstein

"If you are searching for perfection in others, then you seek disappointment. If you seek perfection in yourself, then you will find failure." - Balboos HaGadol Mar 2010

David ONeil

A more positive story about wildlife: Eagle's Nest Township, Minnesota had/(has?) a different relationship with bears. If you don't want to listen to a program, Salon did an article on him as well.

The forgotten roots of science | C++ Programming | DWinLib

RustyF

At the end of the day, it’s a way to implement your public interface to the world without your clients being exposed to the details. You have many options to implement that interface; code directly in the class, delegating to others (composition) or inheriting it. Imagine parallel universes, there is the public one that clients exist in and another that the non-public stuff lives in. Both (potentially) have a need for inheritance either to represent a natural taxonomy (CheckingAccount isa Account, etc) or for reuse (Account inherits Persistent, Equatable). I say “potentially” because out of all the ways to implement your public interface, inheritance is by far the worst in my opinion - it’s the road to spaghetti code ;).