ERC-223 トークン標準

pragma solidity ^0.8.19;
abstract contract IERC223Recipient {
    function tokenReceived(address _from, uint _value, bytes memory _data) public virtual;
}
contract VeryBasicERC223Token {
    event Transfer(address indexed from, address indexed to, uint value, bytes data);
    string  private _name;
    string  private _symbol;
    uint8   private _decimals;
    uint256 private _totalSupply;
    mapping(address => uint256) private balances;
    function name() public view returns (string memory) { return _name; }
    function symbol() public view returns (string memory) {return _symbol; }
    function decimals() public view returns (uint8) { return _decimals; }
    function totalSupply() public view returns (uint256) { return _totalSupply; }
    function balanceOf(address _owner) public view returns (uint256) { return balances[_owner]; }
    function isContract(address account) internal view returns (bool) {
        uint256 size;
        assembly { size := extcodesize(account) }
        return size > 0;
    }
    function transfer(address _to, uint _value, bytes calldata _data) public returns (bool success){
        balances[msg.sender] = balances[msg.sender] - _value;
        balances[_to] = balances[_to] + _value;
        if(isContract(_to)) {
            IERC223Recipient(_to).tokenReceived(msg.sender, _value, _data);
        }
        emit Transfer(msg.sender, _to, _value, _data);
        return true;
    }
    function transfer(address _to, uint _value) public returns (bool success){
        bytes memory _empty = hex"00000000";
        balances[msg.sender] = balances[msg.sender] - _value;
        balances[_to] = balances[_to] + _value;
        if(isContract(_to)) {
            IERC223Recipient(_to).tokenReceived(msg.sender, _value, _empty);
        }
        emit Transfer(msg.sender, _to, _value, _empty);
        return true;
    }
}

contract RecipientContract is IERC223Recipient {
    event Deposit(address whoSentTheTokens);
    uint256 deposits = 0;
    address tokenA; // 受け入れる唯一のトークン。
    function tokenReceived(address _from, uint _value, bytes memory _data) public override
    {
        // この関数内では以下のことを理解しておくことが重要です。
        // msg.sender は受信しているトークンのアドレスであり、
        // ほとんどの場合、トークンコントラクトはイーサを所有または送信しないため、msg.value は常に 0 であり、
        // _from はトークン送金の送信者であり、
        // _value は預け入れられたトークンの量です。
        require(msg.sender == tokenA);
        deposits += _value;
        emit Deposit(_from);
    }
}

contract RecipientContract is IERC223Recipient {
    event Foo();
    event Bar(uint256 someNumber);
    address tokenA; // 受け入れる唯一のトークン。
    function tokenReceived(address _from, uint _value, bytes memory _data) public override
    {
        require(msg.sender == tokenA);
        address(this).call(_data); // 受信したトランザクションを処理し、後続の関数呼び出しを実行します。
    }
    function foo() public
    {
        emit Foo();
    }
    function bar(uint256 _someNumber) public
    {
        emit Bar(_someNumber);
    }
}