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       1                 :             : // SPDX-License-Identifier: MIT
       2                 :             : pragma solidity ^0.8.10;
       3                 :             : 
       4                 :             : /**
       5                 :             :  * @title VersionedInitializable
       6                 :             :  * @author Aave, inspired by the OpenZeppelin Initializable contract
       7                 :             :  * @notice Helper contract to implement initializer functions. To use it, replace
       8                 :             :  * the constructor with a function that has the `initializer` modifier.
       9                 :             :  * @dev WARNING: Unlike constructors, initializer functions must be manually
      10                 :             :  * invoked. This applies both to deploying an Initializable contract, as well
      11                 :             :  * as extending an Initializable contract via inheritance.
      12                 :             :  * WARNING: When used with inheritance, manual care must be taken to not invoke
      13                 :             :  * a parent initializer twice, or ensure that all initializers are idempotent,
      14                 :             :  * because this is not dealt with automatically as with constructors.
      15                 :             :  */
      16                 :             : abstract contract VersionedInitializable {
      17                 :             :   /**
      18                 :             :    * @dev Indicates that the contract has been initialized.
      19                 :             :    */
      20                 :             :   uint256 private lastInitializedRevision = 0;
      21                 :             : 
      22                 :             :   /**
      23                 :             :    * @dev Indicates that the contract is in the process of being initialized.
      24                 :             :    */
      25                 :             :   bool private initializing;
      26                 :             : 
      27                 :             :   /**
      28                 :             :    * @dev Modifier to use in the initializer function of a contract.
      29                 :             :    */
      30                 :             :   modifier initializer() {
      31                 :      346987 :     uint256 revision = getRevision();
      32                 :      346987 :     require(
      33                 :             :       initializing || isConstructor() || revision > lastInitializedRevision,
      34                 :             :       'Contract instance has already been initialized'
      35                 :             :     );
      36                 :             : 
      37                 :      345986 :     bool isTopLevelCall = !initializing;
      38                 :      345986 :     if (isTopLevelCall) {
      39                 :      345986 :       initializing = true;
      40                 :      345986 :       lastInitializedRevision = revision;
      41                 :             :     }
      42                 :             : 
      43                 :             :     _;
      44                 :             : 
      45                 :      344984 :     if (isTopLevelCall) {
      46                 :      344984 :       initializing = false;
      47                 :             :     }
      48                 :             :   }
      49                 :             : 
      50                 :             :   /**
      51                 :             :    * @notice Returns the revision number of the contract
      52                 :             :    * @dev Needs to be defined in the inherited class as a constant.
      53                 :             :    * @return The revision number
      54                 :             :    */
      55                 :             :   function getRevision() internal pure virtual returns (uint256);
      56                 :             : 
      57                 :             :   /**
      58                 :             :    * @notice Returns true if and only if the function is running in the constructor
      59                 :             :    * @return True if the function is running in the constructor
      60                 :             :    */
      61                 :             :   function isConstructor() private view returns (bool) {
      62                 :             :     // extcodesize checks the size of the code stored in an address, and
      63                 :             :     // address returns the current address. Since the code is still not
      64                 :             :     // deployed when running a constructor, any checks on its code size will
      65                 :             :     // yield zero, making it an effective way to detect if a contract is
      66                 :             :     // under construction or not.
      67                 :      346987 :     uint256 cs;
      68                 :             :     //solium-disable-next-line
      69                 :             :     assembly {
      70                 :      346987 :       cs := extcodesize(address())
      71                 :             :     }
      72                 :      346987 :     return cs == 0;
      73                 :             :   }
      74                 :             : 
      75                 :             :   // Reserved storage space to allow for layout changes in the future.
      76                 :             :   uint256[50] private ______gap;
      77                 :             : }