fork download

#include <iostream>
#include <vector>
#include <memory>
 
class MatrixInterface
{
public:
	virtual ~MatrixInterface() = default;
 
	virtual void doSomething() const = 0;
 
	virtual MatrixInterface doSomethingElse() const = 0;
};
 
template<int rows, int cols> class MatrixA : public MatrixInterface
{
public:
	void doSomething() const override
	{
		std::cout << "This is MatrixA... Rows:" << rows << "Cols:" << cols << std::endl;
	}
 
	MatrixA<rows, cols> doSomethingElse() const override
	{
		return MatrixA<rows, cols>();
	}
};
 
template<int rows, int cols>class MatrixB : public MatrixInterface
{
	void doSomething() const override
	{
		std::cout << "This is MatrixB... Rows:" << rows << "Cols:" << cols << std::endl;
	}
};
 
template<int rows, int cols>class MatrixC : public MatrixInterface
{
	void doSomething() const override
	{
		std::cout << "This is MatrixC... Rows:" << rows << "Cols:" << cols << std::endl;
	}
};
 
int main() {
	using VectorType = std::vector<std::unique_ptr<MatrixInterface>>;
	VectorType matricies;
 
	matricies.push_back(VectorType::value_type(new MatrixA<3, 4>));
	matricies.push_back(VectorType::value_type(new MatrixB<5, 6>));
	matricies.push_back(VectorType::value_type(new MatrixC<7, 8>));
 
	for(auto& element : matricies)
	{
		element->doSomething();
	}
 
	return 0;
}

prog.cpp:12:26: error: invalid abstract return type for member function ‘virtual MatrixInterface MatrixInterface::doSomethingElse() const’
  virtual MatrixInterface doSomethingElse() const = 0;
                          ^
prog.cpp:5:7: note:   because the following virtual functions are pure within ‘MatrixInterface’:
 class MatrixInterface
       ^
prog.cpp:10:15: note: 	virtual void MatrixInterface::doSomething() const
  virtual void doSomething() const = 0;
               ^
prog.cpp:12:26: note: 	virtual MatrixInterface MatrixInterface::doSomethingElse() const
  virtual MatrixInterface doSomethingElse() const = 0;
                          ^
prog.cpp: In instantiation of ‘class MatrixA<3, 4>’:
prog.cpp:49:49:   required from here
prog.cpp:23:22: error: invalid covariant return type for ‘MatrixA<rows, cols> MatrixA<rows, cols>::doSomethingElse() const [with int rows = 3; int cols = 4]’
  MatrixA<rows, cols> doSomethingElse() const override
                      ^
prog.cpp:12:26: error:   overriding ‘virtual MatrixInterface MatrixInterface::doSomethingElse() const’
  virtual MatrixInterface doSomethingElse() const = 0;
                          ^
prog.cpp: In function ‘int main()’:
prog.cpp:50:49: error: cannot allocate an object of abstract type ‘MatrixB<5, 6>’
  matricies.push_back(VectorType::value_type(new MatrixB<5, 6>));
                                                 ^
prog.cpp:29:35: note:   because the following virtual functions are pure within ‘MatrixB<5, 6>’:
 template<int rows, int cols>class MatrixB : public MatrixInterface
                                   ^
prog.cpp:12:26: note: 	virtual MatrixInterface MatrixInterface::doSomethingElse() const
  virtual MatrixInterface doSomethingElse() const = 0;
                          ^
prog.cpp:51:49: error: cannot allocate an object of abstract type ‘MatrixC<7, 8>’
  matricies.push_back(VectorType::value_type(new MatrixC<7, 8>));
                                                 ^
prog.cpp:37:35: note:   because the following virtual functions are pure within ‘MatrixC<7, 8>’:
 template<int rows, int cols>class MatrixC : public MatrixInterface
                                   ^
prog.cpp:12:26: note: 	virtual MatrixInterface MatrixInterface::doSomethingElse() const
  virtual MatrixInterface doSomethingElse() const = 0;
                          ^

Standard output is empty