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Constructor of struct calling the member function of another class declared as a pointer

August 9, 2022

I have the following code:

class Cohomology;

struct EMField
{
     std::unique_ptr<Cohomology> coh;
     std::array<DIM> data;

     EMField() {coh -> initializeField(*this);};
}

class Cohomology
{
     private:
        // private members
     public:
        Cohomology(PList params)
        {
             // Constructor of the class
        }

        void initializeField(EMField& field)
        {
             field.coh.reset(this);
             // other methods to initialize field.data using the private members
        }
}

In this answer it is explained that calling a method of an incomplete type is not possible, nor dereferencing the pointer.

In fact, when I try to compile it I get:

warning: invalid use of incomplete type ‘class Cohomology‘

note: forward declaration of ‘class Cohomology‘

My question is: How can I delegate the construction of EMField to the Cohomology class if I cannot use a member of std::unique_ptr<Cohomology> coh ?

>Solution :

Just move the definition of EMField::EMField() until after both classes have been defined.

class Cohomology;

struct EMField
{
     std::unique_ptr<Cohomology> coh;
     std::array<DIM> data;

     EMField();
};

class Cohomology
{
     private:
        // private members
     public:
        Cohomology(PList params)
        {
             // Constructor of the class
        }

        void initializeField(EMField& field)
        {
             field.coh.reset(this);
             // other methods to initialize field.data using the private members
        }
};

inline EMField::EMField()
{
    coh -> initializeField(*this);
}