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55 lines
2.0 KiB
55 lines
2.0 KiB
// SPDX-License-Identifier: MIT
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// solhint-disable-next-line compiler-version
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pragma solidity >=0.4.24 <0.8.0;
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import "../utils/Address.sol";
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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 {UpgradeableProxy-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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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 || _isConstructor() || !_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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/// @dev Returns true if and only if the function is running in the constructor
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function _isConstructor() private view returns (bool) {
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return !Address.isContract(address(this));
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}
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}
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