#include <memory>
#include <shared_mutex>
#include <optional>

struct Data
{
   std::optional<int> i;
};

struct DataHolder
{
   auto getLockedData()
   {
       auto deleter = [lock = std::unique

struct Data
{
   std::optional<int> i;
};

struct DataHolder
{
   auto getLockedData()
   {
       auto deleter = [lock = std::unique_lock<std::mutex>(m)] (Data *) mutable {};
       return std::unique_ptr<Data, decltype(deleter)>{&data, std::move(deleter)};
   }
   
   auto getLockedData() const
   {
       auto deleter = [lock = std::unique_lock<std::mutex>(m)] (const Data *) mutable {};
       return std::unique_ptr<const Data, decltype(deleter)>{&data, std::move(deleter)};
   }

private :
   mutable std::mutex m;
   Data data;
};


int main()
{
   DataHolder d;
   auto producer = [&d]
   {
       auto lockedData = d.getLockedData();
       lockedData->i = 123;
       lockedData.reset();
       while(true);
   };
   auto consumer = [&d = std::as_const(d)]
   {
       for (;;) {
           if (const auto i = d.getLockedData()->i) {
               std::cout << *i << std::endl;
               return;
           }
       }
   };
   std::thread p(producer);
   std::thread c(consumer);…

#include <memory>
#include <shared_mutex>
#include <optional>

struct Data
{
   std::optional<int> i;
};

struct DataHolder
{
   auto getLockedData()
   {
       auto deleter = [lock = std::unique