C++ has unnamed classes!

output

clang version 6.0.0-1ubuntu2 (tags/RELEASE_600/final)
The message is 1 `action` 2 is 3
The (int) sum is 3
The message is 3.000000 `action` 2.000000 is 1.000000
The (float) difference is 1

shim.cpp

#include <iostream>
#include <string>
#include <functional>

template<typename T>
class Contact
{
  public:

  virtual ~Contact() {}
  virtual void Message(std::string) = 0;
  virtual void Report(T) = 0;
};

using IntAction = std::function<int(int, int)>;
using FltAction = std::function<float(float, float)>;

template<typename B, typename A, typename C>
class Machine
{
  public:

  Machine(C c_) : c(c_)
  {}

  void actionAndReport(B n, B m, A a)
  {
    c.Message(std::to_string(n) + " `action` " +
              std::to_string(m) + " is " + std::to_string(a(n, m)));

    c.Report(a(n, m));
  }

  C c;
};

using Messenger    = std::function<void(std::string)>;
using IntReporter  = std::function<void(int)>;
using FltReporter  = std::function<void(float)>;

template<typename I, typename R>
auto make_contact_shim(Messenger m, R r)
{
  class : Contact<I> {
    public:

    void Message(std::string s) override
    {
      m(s);
    }

    void Report(I i) override
    {
      r(i);
    }

    Messenger m;
    R r;

  } c;

  c.m = m;
  c.r = r;

  return c;
}

int main() {

  auto c = make_contact_shim<int, IntReporter>(
    [=](std::string s)
    {
      std::cout << "The message is " << s << std::endl;
    },
    [=](int i)
    {
      std::cout << "The (int) sum is " << i << std::endl;
    }
  );

  Machine<int, IntAction, decltype(c)> machine(c);

  machine.actionAndReport(1, 2, [=](int a, int b)
  {
    return a + b;
  });

  auto c2 = make_contact_shim<float, FltReporter>(
    [=](std::string s)
    {
      std::cout << "The message is " << s << std::endl;
    },
    [=](float i)
    {
      std::cout << "The (float) difference is " << i << std::endl;
    }
  );

  Machine<float, FltAction, decltype(c2)> machine2(c2);

  machine2.actionAndReport(3.0, 2.0, [=](float a, float b)
  {
    return a - b;
  });
}