Finally.h

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/** @noop License Comment
 *  @file
 *  @copyright
 *  This Source Code is subject to the terms of the Mozilla Public License, v2.0.
 *  If a copy of the MPL was not distributed with this file You can obtain one at
 *  https://mozilla.org/MPL/2.0/
 *  
 *  @author David Mórász
 *  @date 2025
 */
 
#pragma once
#include "CoreMinimal.h"
 
namespace Mcro::Finally
{
    /**
     *  @brief
     *  Run arbitrary finalizers on destruction. It has similar purpose to `ON_SCOPE_EXIT`, however FFinally can be
     *  moved around into different scopes, Payload will be only executed if the finalizer hasn't been moved from,
     *  otherwise the payload will be ignored in the source of move assignments
     *
     *  Usage:
     *  @code
     *  {
     *      FFinally fin([] {...})
     *      Async(EAsyncExecution::ThreadPool, [fin = MoveTemp(fin)]
     *      {
     *          // Payload is executed at the end of this scope
     *      }
     *      // Payload is not executed here
     *  }
     *  @endcode
     *  Finalizers can be moved into nested scopes
     *  @code
     *  {
     *      FFinally fin([] {...})
     *      Async(EAsyncExecution::ThreadPool, [fin = MoveTemp(fin)] mutable
     *      {
     *          AsyncTask(ENamedThreads::GameThread, [fin = MoveTemp(fin)]
     *          {
     *              // Payload is executed at the end of this scope
     *          }
     *          // Payload is not executed here
     *      }
     *      // Payload is not executed here
     *  }
     *  @endcode 
     */
    struct FFinally : FNoncopyable
    {
    private:
        TUniqueFunction<void()> Payload;
        bool bIsValid = true;
    
    public:
        FFinally(TUniqueFunction<void()>&& payload) : Payload(MoveTemp(payload)) {}
        FFinally(FFinally&& from) noexcept : Payload(MoveTemp(from.Payload))
        {
            from.bIsValid = false;
        }
        FFinally(FFinally&& from) noexcept : Payload(MoveTemp(from.Payload)) {…}
    
        ~FFinally()
        {
            if(bIsValid) Payload();
        }
        ~FFinally() {…}
    };
    struct FFinally : FNoncopyable {…};
 
    /**
     *  @warning
     *  Do not use this directly, use FINALLY macro. Similar intentions to ON_SCOPE_EXIT but gives more freedom
     */
    struct FFinallySyntaxSupport
    {
        FFinally operator+(TUniqueFunction<void()>&& payload)
        {
            return FFinally(MoveTemp(payload));
        }
        FFinally operator+(TUniqueFunction<void()>&& payload) {…}
    };
    struct FFinallySyntaxSupport {…};
}
namespace Mcro::Finally {…}
 
/**
 *  A more convenient way to use `FFinally`.
 *
 *  @code
 *  auto fin = FINALLY(=, this) mutable
 *  {
 *      ...
 *  };
 *  AsyncTask(ENamedThreads::GameThread, [fin = MoveTemp(fin)]
 *  {
 *      // Payload is executed at the end of this scope
 *  }
 *  @endcode 
 */
#define FINALLY(...) Mcro::Finally::FFinallySyntaxSupport() + [__VA_ARGS__]()