Ховнокод с попыткой реализовать паттерн Композит в плюсах

composite_bad.cpp

#include <cstdio>
#include <vector>
#include <iostream>
using namespace std;

struct Neuron
{
  vector<Neuron*> in, out;
  unsigned int id;

  Neuron()
  {
    static int id = 1;
    this->id = id++;
  }

  template <typename T> void connect_to(T& other)
  {
    for (Neuron& to : other)
      connect_to(other);
  }

  template<> void connect_to<Neuron>(Neuron& other)
  {
    out.push_back(&other);
    other.in.push_back(this);
  }

  // connect_to(vector<Neuron>&)
  
  Neuron* begin() { return this; }
  Neuron* end()   { return this + 1; }

  friend ostream& operator<<(ostream& os, const Neuron& obj)
  {
    for (Neuron* n : obj.in)
    {
      os << n->id << "\t-->\t[" << obj.id << "]" << endl;
    }

    for (Neuron* n : obj.out)
    {
      os << "[" << obj.id << "]\t-->\t" << n->id << endl;
    }
    return os;
  }
};

struct NeuronLayer : vector<Neuron>
{
  NeuronLayer(int count)
  {
    while (count-- > 0)
      emplace_back(Neuron{});
  }

  template <typename T> void connect_to(T& other)
  {
    for (Neuron& from : *this) // not this
      for (Neuron& to : other)
        from.connect_to(to);
  }

  friend ostream& operator<<(ostream& os, const NeuronLayer& obj)
  {
    for (auto& n : obj) os << n;
    return os;
  }
};

int main()
{
  Neuron n1, n2;
  n1.connect_to(n2);

  cout << n1 << n2 << endl;

  NeuronLayer l1{5};
  Neuron n3;
  l1.connect_to(n3);
  
  cout << "Neuron " << n3.id << endl << n3 << endl;
  cout << "Layer " << endl << l1 << endl;

  NeuronLayer l2{ 2 }, l3{ 3 };
  l2.connect_to(l3);
  cout << "Layer l2" << endl << l2;
  cout << "Layer l3" << endl << l3;

  getchar();
  return 0;
}