Once.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::Once
{
    /** <pre>
     * Used for lambdas which supposed to run only once. The first time it is converted to bool it returns true
     * but every other times it will return false.
     * 
     * Usage:
     * 
     * using namespace BaseUtils;
     * SomeEvent.AddLambda([once = FOnce()]
     * {
     *     // Just use it inside a condition
     *     if (once) { ... }
     *     
     *     // exploiting short-circuit:
     *     if (MyCondition && once) { ... }
     *
     *     // but this will not produce the expected result:
     *     if (once && MyCondition) { ... } // BAD
     * }
     * </pre>
     */
    struct FOnce
    {
    private:
        bool bIsValid = true;
        
    public:
        FORCEINLINE FOnce() {}
        FORCEINLINE FOnce(const FOnce& from) : bIsValid(from.bIsValid) {}
        FORCEINLINE FOnce(FOnce&& from) noexcept
        {
            from.bIsValid = false;
        }
 
        FORCEINLINE operator bool()
        {
            const bool result = bIsValid;
            bIsValid = false;
            return result;
        }
 
        FORCEINLINE bool IsTriggered() const
        {
            return !bIsValid;
        }
 
        FORCEINLINE void Reset()
        {
            bIsValid = true;
        }
    };
}