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I have taken the snippet of code below from a tutorial made in 2018 for making an ERC-20 contract.

However when I followed all the steps I got an error which I will share below.

Code Snippet:

pragma solidity ^0.8.9;
import "../node_modules/openzeppelin-solidity/contracts/token/ERC20/ERC20.sol";
contract sampleToken is ERC20 
{
string public name = "ExampleToken";
string public symbol = "EGT";
uint public decimals = 18;
uint public INITIAL_SUPPLY = 10000 * (10 ** decimals);
constructor() public 
    {
_totalSupply = INITIAL_SUPPLY;
_balances[msg.sender] = INITIAL_SUPPLY;
    }
}

Error:

"message": "Undeclared identifier. Did you mean \"totalSupply"\?`
{
    "resource": "/Users/hassan/Desktop/Blockchain/blockchain/contracts/sampleToken.sol",
    "owner": "_generated_diagnostic_collection_name_#0",
    "severity": 8,
    "message": "Undeclared identifier.",
    "startLineNumber": 12,
    "startColumn": 1,
    "endLineNumber": 12,
    "endColumn": 10
}

Why is this code not valid anymore? How to fix it?

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  • This is not a question about what breaking changes happened in Solidity. This is a specific issue related to how to work with the latest implementation of ERC20 provided by OpenZeppelin. Nov 4, 2021 at 6:54

1 Answer 1

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_totalSupply is defined as a private storage variable in the ERC20 contract:

uint256 private _totalSupply;

Thus no contract, not even child contract like yours, can write directly to _totalSupply.

If you want to mint a specific amount of tokens in the constructor, you have to use the _mint function.

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