C ++ functor passing through recursion: "attempt to use a remote function"

Question

Context

Grade a course for data structures and algorithms, exercise in using the AVL tree and hash tables to analyze input to create a dictionary file, and then use this file to perform spellchecking.
NB: I do not ask for help in solving this problem, which is not something that is difficult for me. I ask for help to understand the aspects of passing / using an object to a C ++ function, which causes me considerable disappointment. This aspect of C ++ is not part of the evaluation, there are no bindings to it, I just have a personal problem sending the code, I don't like the design.

Problem

Passing a functor to a recursive function results in a compiler error, "attempt to use a remote function." I thought this was a problem with passing a functor by value, so I changed the parameter for passing by reference, which gives "an inappropriate member function to call the <public member function from the AVL tree that starts the recursion>," in this case I don’t I know how to change a function declaration to fit. I also tried to make the parameter: const UnaryFunction& action(permalink to object-object), but this gives a compiler error " no matching function for call to object of type 'const std::__1::__mem_fn<void (DictGen::*)(std::__1::basic_string<char> &)>'", in which case I can not understand why it will not match DictGen :: output signature.

the code

Relevant parts of tree tree AVL:

template <class T>
struct AVLNode
{ // simple data carrier node for AVL tree
    AVLNode<T>* lChild;
    AVLNode<T>* rChild;
    AVLBalance balFac;
    T data;
};

template <class T>
class AVLTree<T>
{
    ...

    AVLNode<T>* root;

    template <class UnaryFunction>
    void inorderAction( AVLNode<T>* node, UnaryFunction action )
    {
        if ( node != NULL )
        {
            inorderAction( node->lChild, action );
            action( node->data ); // << problem line
            inorderAction( node->rChild, action );
        }
    }

public:
    template <class UnaryFunction>
    void inorder( UnaryFunction action )
    {
        inorderAction( root, action );
    }
}

Relevant parts of the DictGen class:

class DictGen
{
    ...

    FILE* outStream;
    AVLTree<std::string> dict;

    void output( std::string& word )
    {
        fprintf( outstream, "%s\n", word.c_str() );
    }

public:
    goGoGadgetDictionaryGenerator()
    {
        ...

        dict.inorder( std::mem_fn( &DictGen::output ) ); // << also problem line
    }
}

Interpretation / Translation

AVL , node, UnaryFunction action. DictGen FILE *, DictGen , -- dict.inorder( ... ).

/

, , , C . , ; DictGen.
- ++-, , . , SO ( -), Google PDF- . , , . , a const UnaryFunction& , , .

, outStream.

, , SO, , ++ , . SO, , .

- ?
- / , ?
?
, , , ?

SO, , , . , , .

Answer 1

++ 11. std::mem_fn std::bind, .

void gen()
{
    dict.inorder(
      [this]( std::string& word ) { this->output(word); }
    );
}

, , std::bind( std::mem_fn( &T::method ), this, std::placeholders::_1)

:

 [capture-list]( arguments )->return value { code }

[=] ( ) [&] ( ) [var1, var2] ( var1 var2 ) [&var1, &var2] ( var1 var2 ) . (++ 1y , [x = std::move(y)])

(arguments) - . , , .

-> return value lambdas lambdas, void. ( ++ 1y )

.

Answer 2

DictGen, -:

    // ...
    void gen()
    {
        dict.inorder(
          std::bind( std::mem_fn( &DictGen::output ), 
                     this,  std::placeholders::_1) );
    }
    // ...