Is it possible to use anonymous classes in C++?

Question

I have seen anonymous classes in C++ code on Quora. It\'s successfully compiled and run.

Code here:

#inclu         


        

Answer 1

In C++, an anonymous union is a union of this form:

 union { ... } ;

It defines an unnamed object of an unnamed type. Its members are injected in the surrounding scope, so one can refer to them without using an <object>. prefix that otherwise would be necessary.

In this sense, no anonymous classes (that are not unions --- in C++ unions are classes) exist.

On the other hand, unnamed classes (including structs and unions) are nothing unusual.

union { ... } x;
class { ... } y;
typedef struct { ... } z;

x and y are named object of unnamed types. z is a typedef-name that is an alias for an unnamed struct. They are not called anonymous because this term is reserved for the above form of a union.

[](){}

Lambdas are unnamed objects of unnamed class types, but they are not called anonymous either.

Answer 2

Not only that, you can create more instances of the class by using decltype.

#include <iostream>

class 
{
   public:
      int val;
} a;


int main()
{
   decltype(a) b;
   a.val = 10;
   b.val = 20;

   std::cout << a.val << std::endl;
   std::cout << b.val << std::endl;
   return 0;
}

Output:

10
20