// msvc compiler options:
// /await /std:c++latest /Zc:__cplusplus
// 64 bit: /await:heapelide
#if __cplusplus && __cplusplus > 201402L
# if __has_include(<experimental/format>)
#  include <experimental/format>
# endif
# if __has_include()
#  include
#  include
using co_suspend_never = std::suspend_never;
# elif __has_include(<experimental/coroutine>)
#  include <experimental/coroutine>
#  include <experimental/generator>
using co_suspend_never = std::experimental::suspend_never;
# else
# error coroutine support expected.
# endif
#else
# error modern cplusplus expected.
#endif



///////////////////////////////////////////////////////////////////
/// utils
///

struct logger
{
 template<typename ...Types>
 static void info(Types&&...types)
 {
   std::cout << "[" << std::this_thread::get_id() << "]";
   ((std::cout << std::forward(types)), ...);
   std::cout << std::endl;
 }
};

struct scope_tracer
{
 const char* const func;
 void* address;
 explicit scope_tracer(const char* func, void* address = nullptr)…