ERC-1155 — multi-token standard

ERC-20 is one token type per contract. ERC-721 is one NFT collection per contract. If your game has 500 item types (swords, potions, shields, currencies), deploying 500 contracts is absurd.

ERC-1155 solves this: one contract, many token IDs, each with a fungible balance.

solidity
// Token ID 1 = gold coins (fungible, millions in circulation)
// Token ID 2 = legendary sword (NFT, supply = 1)
// Token ID 3 = health potion (fungible, stackable)

solidity
import "@openzeppelin/contracts/token/ERC1155/ERC1155.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

contract GameItems is ERC1155, Ownable {
    uint256 public constant GOLD = 0;
    uint256 public constant SWORD = 1;
    uint256 public constant SHIELD = 2;

    constructor() ERC1155("https://game.example/{id}.json") Ownable(msg.sender) {
        _mint(msg.sender, GOLD, 10**24, "");
        _mint(msg.sender, SWORD, 100, "");
        _mint(msg.sender, SHIELD, 50, "");
    }
}

ERC-1155 supports moving multiple token types in one tx via safeBatchTransferFrom. Gas-efficient for games where a trade involves multiple items.

ERC1155("https://.../{id}.json") — the {id} placeholder is a 64-char hex-padded token ID. Example: https://game.example/0000...0001.json for token ID 1.

Write CardDeck using OZ's ERC1155. Define three constants: SPADES=0, HEARTS=1, CLUBS=2. In the constructor, mint 52 of each to the deployer.