Standar Multi-Token ERC-1155

Why ERC-1155 Exists

Token IDs as Categories

Core Balance Mapping

mapping(uint256 => mapping(address => uint256)) private _balances;

function balanceOf(address account, uint256 id) public view returns (uint256) {
    return _balances[id][account];
}

Batch Balance Queries

function balanceOfBatch(address[] memory accounts, uint256[] memory ids)
    public view returns (uint256[] memory)
{
    require(accounts.length == ids.length, 'length mismatch');
    uint256[] memory batch = new uint256[](accounts.length);
    for (uint256 i = 0; i < accounts.length; i++) {
        batch[i] = _balances[ids[i]][accounts[i]];
    }
    return batch;
}

Batch Transfers

function safeBatchTransferFrom(
    address from,
    address to,
    uint256[] memory ids,
    uint256[] memory amounts,
    bytes memory data
) public {
    require(ids.length == amounts.length, 'length mismatch');
    for (uint256 i = 0; i < ids.length; i++) {
        _balances[ids[i]][from] -= amounts[i];
        _balances[ids[i]][to] += amounts[i];
    }
}

Approval For All

mapping(address => mapping(address => bool)) private _operatorApprovals;

function setApprovalForAll(address operator, bool approved) public {
    _operatorApprovals[msg.sender][operator] = approved;
}

function isApprovedForAll(address owner, address operator) public view returns (bool) {
    return _operatorApprovals[owner][operator];
}

The Shared Metadata URI

string private _uri = 'https://game.example/api/{id}.json';

function uri(uint256) public view returns (string memory) {
    return _uri;
}

Minting Tokens

function _mint(address to, uint256 id, uint256 amount) internal {
    require(to != address(0), 'mint to zero');
    _balances[id][to] += amount;
    emit TransferSingle(msg.sender, address(0), to, id, amount);
}

event TransferSingle(address operator, address from, address to, uint256 id, uint256 value);

Safe Transfer Receiver Check

interface IERC1155Receiver {
    function onERC1155Received(
        address operator, address from,
        uint256 id, uint256 value, bytes calldata data
    ) external returns (bytes4);
}

Using OpenZeppelin

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import '@openzeppelin/contracts/token/ERC1155/ERC1155.sol';

contract GameItems is ERC1155 {
    uint256 public constant GOLD = 0;
    uint256 public constant SWORD = 1;

    constructor() ERC1155('https://game.example/api/{id}.json') {
        _mint(msg.sender, GOLD, 1000, '');
        _mint(msg.sender, SWORD, 1, '');
    }
}

When To Choose ERC-1155

Quick Check

Recap