web3-starter-sol/basic_knowledge/token_standards/erc777.md

ERC777

• an ERC20-compatible interface
• transfer tokens using a send function, similar to ether transfers
• compatible with ERC820 for token contract registration
• allow contracts and addresses to control which tokens they send through a tokensToSend function that is called prior to sending
• enable contracts and addresses to be notified of the tokens' receipt by calling a tokensReceived function in the recipient, and to reduce the probability of tokens being locked into contracts by requiring contracts to provide a tokensReceived function
• allow existing contracts to use proxy contracts for the tokensToSend and tokensReceived` functions
• operate in the same way whether sending to a contract or an EOA
• provide specific events for the minting and burning of tokens
• enable operators (trusted third parties, intended to be verified contracts) to move tokens on behalf of a token holder
• provide metadata on token transfer transactions in userData and operatorData fields

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ERC777 contract interface specification

interface ERC777Token {
    function name() public constant returns (string);
    function symbol() public constant returns (string);
    function totalSupply() public constant returns (uint256);
    function granularity() public constant returns (uint256);
    function balanceOf(address owner) public constant returns (uint256);

    function send(address to, uint256 amount, bytes userData) public;

    function authorizeOperator(address operator) public;
    function revokeOperator(address operator) public;
    function isOperatorFor(address operator, address tokenHolder)
        public constant returns (bool);
    function operatorSend(address from, address to, uint256 amount,
                          bytes userData,bytes operatorData) public;

    event Sent(address indexed operator, address indexed from,
               address indexed to, uint256 amount, bytes userData,
               bytes operatorData);
    event Minted(address indexed operator, address indexed to,
                 uint256 amount, bytes operatorData);
    event Burned(address indexed operator, address indexed from,
                 uint256 amount, bytes userData, bytes operatorData);
    event AuthorizedOperator(address indexed operator,
                             address indexed tokenHolder);
    event RevokedOperator(address indexed operator, address indexed tokenHolder);
}