Contract module which provides a basic access control mechanism, where there is an account (an owner) that can be granted exclusive access to specific functions. By default, the owner account will be the one that deploys the contract. This can later be changed with {transferOwnership}. This module is used through inheritance. It will make available the modifier `onlyOwner`, which can be applied to your functions to restrict their use to the owner.

Contract module which allows children to implement an emergency stop mechanism that can be triggered by an authorized account. This module is used through inheritance. It will make available the modifiers `whenNotPaused` and `whenPaused`, which can be applied to the functions of your contract. Note that they will not be pausable by simply including this module, only once the modifiers are put in place.

These functions deal with verification of Merkle Tree proofs. The tree and the proofs can be generated using our https://github.com/OpenZeppelin/merkle-tree[JavaScript library]. You will find a quickstart guide in the readme. WARNING: You should avoid using leaf values that are 64 bytes long prior to hashing, or use a hash function other than keccak256 for hashing leaves. This is because the concatenation of a sorted pair of internal nodes in the merkle tree could be reinterpreted as a leaf value. OpenZeppelin's JavaScript library generates merkle trees that are safe against this attack out of the box.

This is a base contract to aid in writing upgradeable contracts, or any kind of contract that will be deployed behind a proxy. Since proxied contracts do not make use of a constructor, it's common to move constructor logic to an external initializer function, usually called `initialize`. It then becomes necessary to protect this initializer function so it can only be called once. The {initializer} modifier provided by this contract will have this effect. The initialization functions use a version number. Once a version number is used, it is consumed and cannot be reused. This mechanism prevents re-execution of each "step" but allows the creation of new initialization steps in case an upgrade adds a module that needs to be initialized. For example: [.hljs-theme-light.nopadding] ``` contract MyToken is ERC20Upgradeable { function initialize() initializer public { __ERC20_init("MyToken", "MTK"); } } contract MyTokenV2 is MyToken, ERC20PermitUpgradeable { function initializeV2() reinitializer(2) public { __ERC20Permit_init("MyToken"); } } ``` TIP: To avoid leaving the proxy in an uninitialized state, the initializer function should be called as early as possible by providing the encoded function call as the `_data` argument to {ERC1967Proxy-constructor}. CAUTION: When used with inheritance, manual care must be taken to not invoke a parent initializer twice, or to ensure that all initializers are idempotent. This is not verified automatically as constructors are by Solidity. [CAUTION] ==== Avoid leaving a contract uninitialized. An uninitialized contract can be taken over by an attacker. This applies to both a proxy and its implementation contract, which may impact the proxy. To prevent the implementation contract from being used, you should invoke the {_disableInitializers} function in the constructor to automatically lock it when it is deployed: [.hljs-theme-light.nopadding] ```

Provides information about the current execution context, including the sender of the transaction and its data. While these are generally available via msg.sender and msg.data, they should not be accessed in such a direct manner, since when dealing with meta-transactions the account sending and paying for execution may not be the actual sender (as far as an application is concerned). This contract is only required for intermediate, library-like contracts.

Collection of functions related to the address type

Implementation of the basic standard multi-token. See https://eips.ethereum.org/EIPS/eip-1155 Originally based on code by Enjin: https://github.com/enjin/erc-1155 _Available since v3.1._

Extension of ERC1155 that adds tracking of total supply per id. Useful for scenarios where Fungible and Non-fungible tokens have to be clearly identified. Note: While a totalSupply of 1 might mean the corresponding is an NFT, there is no guarantees that no other token with the same id are not going to be minted.

Required interface of an ERC1155 compliant contract, as defined in the https://eips.ethereum.org/EIPS/eip-1155[EIP]. _Available since v3.1._

_Available since v3.1._

Interface of the optional ERC1155MetadataExtension interface, as defined in the https://eips.ethereum.org/EIPS/eip-1155#metadata-extensions[EIP]. _Available since v3.1._

Implementation of the {IERC165} interface. Contracts that want to implement ERC165 should inherit from this contract and override {supportsInterface} to check for the additional interface id that will be supported. For example: ```solidity function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) { return interfaceId == type(MyInterface).interfaceId || super.supportsInterface(interfaceId); } ``` Alternatively, {ERC165Storage} provides an easier to use but more expensive implementation.

Interface of the ERC165 standard, as defined in the https://eips.ethereum.org/EIPS/eip-165[EIP]. Implementers can declare support of contract interfaces, which can then be queried by others ({ERC165Checker}). For an implementation, see {ERC165}.