Abstract class and unique pointer

Question

I have the following error in my code:

error: allocating an object of abstract class type \'Material\'

I don\'t know how to handle this case.

Answer 1

This call:

std::make_unique(mat1)

tries to create an instance of class Material, it is irrelevant what type mat1 has. You seem to need method clone() in your class:

class Material {
...
    virtual std::unique_ptr clone() const = 0;
};

then Mix ctor would be:

Mix(const Material& mat1, const Material& mat2)
    : mat1_(mat1.clone())
    , mat2_(mat2.clone())
  {}

and you need to implement clone() in every derived class:

struct Basic : public Material
{
  Basic() = default;

  virtual std::unique_ptr clone() const override
  {
      return std::make_unique( *this ); 
  }

  virtual int get_color() const override
  {
    return 1;
  }
};