invalid initialization of reference of type 'template class' from 'inherit class'

Question

I am developing the following class, that inherits a template class.

template<typename T>
class test : public T
{
 public:
   void init() {
     T::init();
     abc = true; 
   }
 private:
   bool abc;
}

On one of my base class I have the following singleton method:

class foo : protected bar
{
public:
   static foo &getInstance();
   void init();       

private:
   foo();
   foo(foo const&);
   void operator=(foo const&);
   ~foo() {};
}

When I create the following instance:

test<foo> &instance = test<foo>::getInstance();

I get an error:

invalid initialization of reference of type test<foo>& from expression of type foo

Do you know what is happening?

Thanks

Answer 1

test<foo>::getInstance() resolves to foo::getInstance() . That function returns a foo& , not a test<foo>& . A foo& cannot be converted to test<foo>& . Hence the compiler error.

Use

foo& instance = test<foo>::getInstance();

If you must have a test<foo>& , you need to implement getInstance() in test .

template<typename T>
class test : public T
{
   public:
      void init() {
         T::init();
         abc = true; 
      }
      static test& getInstance()
      {
         static test instance;
         return instance;
      }

   private:
      bool abc;
};

But then, you'll have to take care of the cascading effects. You'll have to make sure that the constructors and destructors of foo are declared as either public or protected . They cannot be private .