Why declare `__gap` variable in ReentrancyGuardUpgradeable.sol?

Smart Contracts
1

Hi,

I would like to know why declaring the __gap variable in ReentrancyGuardUpgradeable.sol.


abstract contract ReentrancyGuardUpgradeable is Initializable {
    // Booleans are more expensive than uint256 or any type that takes up a full
    // word because each write operation emits an extra SLOAD to first read the
    // slot's contents, replace the bits taken up by the boolean, and then write
    // back. This is the compiler's defense against contract upgrades and
    // pointer aliasing, and it cannot be disabled.

    // The values being non-zero value makes deployment a bit more expensive,
    // but in exchange the refund on every call to nonReentrant will be lower in
    // amount. Since refunds are capped to a percentage of the total
    // transaction's gas, it is best to keep them low in cases like this one, to
    // increase the likelihood of the full refund coming into effect.
    uint256 private constant _NOT_ENTERED = 1;
    uint256 private constant _ENTERED = 2;

    uint256 private _status;

    function __ReentrancyGuard_init() internal initializer {
        __ReentrancyGuard_init_unchained();
    }

    function __ReentrancyGuard_init_unchained() internal initializer {
        _status = _NOT_ENTERED;
    }

    /**
     * @dev Prevents a contract from calling itself, directly or indirectly.
     * Calling a `nonReentrant` function from another `nonReentrant`
     * function is not supported. It is possible to prevent this from happening
     * by making the `nonReentrant` function external, and make it call a
     * `private` function that does the actual work.
     */
    modifier nonReentrant() {
        // On the first call to nonReentrant, _notEntered will be true
        require(_status != _ENTERED, "ReentrancyGuard: reentrant call");

        // Any calls to nonReentrant after this point will fail
        _status = _ENTERED;

        _;

        // By storing the original value once again, a refund is triggered (see
        // https://eips.ethereum.org/EIPS/eip-2200)
        _status = _NOT_ENTERED;
    }
    
    uint256[49] private __gap;
}

It is assumed that I only use this contract to prevent a reentrancy attack and I do not use the __gap variable. so It obviously spent more on storage and gas fee. so I would like to know the effect of this variable. is it if worthly to be used.

2

That array that has been assigned at the bottom of your script above.
It does not exist within open zeppelins template.

See here >

The array you pointed out must be related to another part of the contract.
Where else can you find __gap ?

3

Oh, I got it. This is the PartyDao contract code. because they used a proxy structure, maybe it is used to prevent storage slot clash. their repo is here:https://github.com/PartyDAO/partybid/tree/main/contracts

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