call_once.h

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#pragma once
#include <utility>
 
namespace xtd {
  struct call_once {
  };
  
  template<typename function_t>
  struct __xtd_call_once_object__ {
    __xtd_call_once_object__(function_t function) { function(); }
  };
  
  template<typename function_t>
  auto operator +(call_once, function_t&& function) {
    return __xtd_call_once_object__<function_t>{std::forward<function_t>(function)};
  }
}
 
#define __xtd_call_once_cat__(name, line) name##line
#define __xtd_call_once_id__(name, line) __xtd_call_once_cat__(name, line)
 
#define call_once_ [[maybe_unused]] static auto __xtd_call_once_id__(__xtd__call_once__, __LINE__) = xtd::call_once {} + [&]