Is it possible to nest coroutines using Boost.Coroutine?

Question

I would like to call a coroutine when already in a coroutine. Is it possible using Boost.Coroutine?

Answer 1

Yes, it's easy as:

#include <iostream>
#include <boost/coroutine/coroutine.hpp>

typedef boost::coroutines::coroutine<int()> generator;

void bar(generator::caller_type& yield)
{
  for (std::size_t i = 100; i < 110; ++i)
    yield(i);
}

void foo(generator::caller_type& yield)
{
  for (std::size_t i = 0; i < 10; ++i)
  {
    generator nested_gen(bar);
    while (nested_gen)
    {
      std::cout << "foo: " << nested_gen.get() << std::endl;
      nested_gen();
    }
    yield(i);
  }
}

int main()
{
  generator gen(foo);
  while (gen)
  {
    std::cout << "main: " << gen.get() << std::endl;
    gen();
  }
  return 0;
};

Edit: With Boost >= 1.56

#include <iostream>
#include <boost/coroutine/asymmetric_coroutine.hpp>

using generator = typename boost::coroutines::asymmetric_coroutine<std::size_t>::pull_type;
using yield_type = typename boost::coroutines::asymmetric_coroutine<std::size_t>::push_type;

void bar(yield_type& yield)
{
  for (std::size_t i = 100; i < 110; ++i)
    yield(i);
}

void foo(yield_type& yield)
{
  for (std::size_t i = 0; i < 10; ++i)
  {
    generator nested_gen{bar};
    while (nested_gen)
    {
      std::cout << "foo: " << nested_gen.get() << '\n';
      nested_gen();
    }
    yield(i);
  }
}

int main()
{
  generator gen{foo};
  while (gen)
  {
    std::cout << "main: " << gen.get() << '\n';
    gen();
  }
  return 0;
};