ERC721AStorage.sol

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

library ERC721AStorage {
    // Bypass for a `--via-ir` bug (https://github.com/chiru-labs/ERC721A/pull/364).
    struct TokenApprovalRef {
        address value;
    }

    struct Layout {
        // =============================================================
        //                            STORAGE
        // =============================================================

        // The next token ID to be minted.
        uint256 _currentIndex;
        // The number of tokens burned.
        uint256 _burnCounter;
        // Token name
        string _name;
        // Token symbol
        string _symbol;
        // Mapping from token ID to ownership details
        // An empty struct value does not necessarily mean the token is unowned.
        // See {_packedOwnershipOf} implementation for details.
        //
        // Bits Layout:
        // - [0..159]   `addr`
        // - [160..223] `startTimestamp`
        // - [224]      `burned`
        // - [225]      `nextInitialized`
        // - [232..255] `extraData`
        mapping(uint256 => uint256) _packedOwnerships;
        // Mapping owner address to address data.
        //
        // Bits Layout:
        // - [0..63]    `balance`
        // - [64..127]  `numberMinted`
        // - [128..191] `numberBurned`
        // - [192..255] `aux`
        mapping(address => uint256) _packedAddressData;
        // Mapping from token ID to approved address.
        mapping(uint256 => ERC721AStorage.TokenApprovalRef) _tokenApprovals;
        // Mapping from owner to operator approvals
        mapping(address => mapping(address => bool)) _operatorApprovals;
    }

    bytes32 internal constant STORAGE_SLOT = keccak256('ERC721A.contracts.storage.ERC721A');

    function layout() internal pure returns (Layout storage l) {
        bytes32 slot = STORAGE_SLOT;
        assembly {
            l.slot := slot
        }
    }
}