nifty_counter.hpp

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#pragma once
 
#include <cstddef>
 
namespace uni20
{
 
template <auto Init, auto Exit = []() noexcept {}>
  requires requires {
    { Init() } noexcept;
    { Exit() } noexcept;
  }
class nifty_counter {
  public:
    nifty_counter() noexcept
    {
      if (count_++ == 0) Init();
    }
 
    nifty_counter(nifty_counter const&) = delete;
    nifty_counter(nifty_counter&&) = delete;
    nifty_counter& operator=(nifty_counter const&) = delete;
    nifty_counter& operator=(nifty_counter&&) = delete;
 
    ~nifty_counter() noexcept
    {
      if (--count_ == 0) Exit();
    }
 
  private:
    static constinit inline std::size_t count_{0};
};
 
} // namespace uni20