In which situation is it useful to have a private constructor for a class?

Question

I wrote a small class using a private constructor:
https://code.sololearn.com/ctcZotz7rpMY/#cs
Could you please answer my questions in the comments of the program?

Answer 1

comupubit well maybe not always at the end of the program (that's just the case for smaller ones), as sometimes the garbage collector sees that you have no more references to the class and just deletes it, but yes the only way to control when an object is deleted is to do it manually.

Answer 2

the destructor is indeed called in both situations, check again, i'm getting

Constructor
Constructor
Destructor
Destructor

as my output.

Answer 3

comupubit the order isn't what you expected because objects are destroyed at the end of program execution unless manually deleted. also, in VS2017 they aren't called because of the Console.ReadLine() which prevents the program from ending and destroying the objects, if you run the program in non-debug mode you can delete the extra ReadLine() command and see that the objects do indeed get destroyed.

Answer 4

@hinanawi:
O.K. That makes sense to me. Thank you again!

Answer 5

@hinanawi:
Thank you! You were right. The destructor is called twice as it should be.

But shouldnt the order be different? Shouldn't the output be like:
Constructor
Destructor
Constructor
Destructor

Also: The strange thing is: When I run the same program in Visual Studio 2017 the destructor is not called at all. I dont understand why.

Answer 6

I already found out that a private copy-constructor (or a cast-constructor) can indeed be useful in some situations.

Answer 7

@hinanawi:
Thank you! I perfectly understood your answer :-) And your answer seems correct to me. So, this means, that the only way to control, when a destructor is called, is to manually delete an object? Otherwise destructors for existing objects are automatically called at the end of the program?