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61 lines
2.2 KiB
61 lines
2.2 KiB
// SPDX-License-Identifier: MIT
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pragma solidity ^0.8.0;
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/**
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* @dev This is a base contract to aid in writing upgradeable contracts, or any kind of contract that will be deployed
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* behind a proxy. Since a proxied contract can't have a constructor, it's common to move constructor logic to an
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* external initializer function, usually called `initialize`. It then becomes necessary to protect this initializer
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* function so it can only be called once. The {initializer} modifier provided by this contract will have this effect.
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*
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* TIP: To avoid leaving the proxy in an uninitialized state, the initializer function should be called as early as
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* possible by providing the encoded function call as the `_data` argument to {ERC1967Proxy-constructor}.
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*
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* CAUTION: When used with inheritance, manual care must be taken to not invoke a parent initializer twice, or to ensure
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* that all initializers are idempotent. This is not verified automatically as constructors are by Solidity.
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*
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* [CAUTION]
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* ====
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* Avoid leaving a contract uninitialized.
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*
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* An uninitialized contract can be taken over by an attacker. This applies to both a proxy and its implementation
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* contract, which may impact the proxy. To initialize the implementation contract, you can either invoke the
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* initializer manually, or you can include a constructor to automatically mark it as initialized when it is deployed:
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*
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* [.hljs-theme-light.nopadding]
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* ```
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* /// @custom:oz-upgrades-unsafe-allow constructor
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* constructor() initializer {}
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* ```
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* ====
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*/
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abstract contract Initializable {
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/**
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* @dev Indicates that the contract has been initialized.
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*/
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bool private _initialized;
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/**
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* @dev Indicates that the contract is in the process of being initialized.
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*/
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bool private _initializing;
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/**
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* @dev Modifier to protect an initializer function from being invoked twice.
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*/
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modifier initializer() {
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require(_initializing || !_initialized, "Initializable: contract is already initialized");
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bool isTopLevelCall = !_initializing;
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if (isTopLevelCall) {
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_initializing = true;
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_initialized = true;
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}
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_;
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if (isTopLevelCall) {
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_initializing = false;
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}
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}
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}
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