Lazy Mint Extension ERC1155

Intro

Another common ask is how to do lazy-minting with Manifold. If you're unfamiliar, lazy-minting is a technique by which minting costs are passed on to the buyer. This makes sense in many situations (especially collectible-style projects), but does not make sense in others. We'll take a look at the contract and how to deploy it here, but I would not suggest doing this for collections of less than, say, 20 tokens. The reason for this is that deploying an extension costs gas! And on a smaller scale, the savings from lazy-minting are less than the cost to deploy the contract.

Anyway, let's take a look. We'll do this with an ERC1155 contract, but something similar can be done with ERC721s.

Contract

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/// @author: manifold.xyz

import "@manifoldxyz/libraries-solidity/contracts/access/AdminControl.sol";
import "@manifoldxyz/creator-core-solidity/contracts/core/IERC1155CreatorCore.sol";
import "@manifoldxyz/creator-core-solidity/contracts/extensions/ICreatorExtensionTokenURI.sol";

import "@openzeppelin/contracts/utils/introspection/ERC165.sol";

contract Tutorial2 is AdminControl, ICreatorExtensionTokenURI{

    address private _core;
    string private _baseURI;

    function initialize(address core) public adminRequired {
      _core = core;

      address[] memory to = new address[](1);
      to[0] = msg.sender;
      uint[] memory amounts = new uint[](1);
      amounts[0] = 1;
      string[] memory uris = new string[](1);
      uris[0] = "";

      IERC1155CreatorCore(_core).mintExtensionNew(to, amounts, uris);
    }

    function mint() public {
      address[] memory to = new address[](1);
      to[0] = msg.sender;
      uint[] memory tokenIds = new uint[](1);
      tokenIds[0] = 1;
      uint[] memory amounts = new uint[](1);
      amounts[0] = 1;

      IERC1155CreatorCore(_core).mintExtensionExisting(to, tokenIds, amounts);
    }

    function supportsInterface(bytes4 interfaceId) public view virtual override(AdminControl, IERC165) returns (bool) {
        return interfaceId == type(ICreatorExtensionTokenURI).interfaceId || AdminControl.supportsInterface(interfaceId) || super.supportsInterface(interfaceId);
    }

    function setBaseURI(string memory baseURI) public adminRequired {
      _baseURI = baseURI;
    }

    function tokenURI(address core, uint256 tokenId) external view override returns (string memory) {
        require(core == _core, "Invalid token");
        return _baseURI;
    }
}

Let's walk through the contract here before we think about deploying it.

The first function we have there is called initialize and this is where we set ourselves up by minting the first copy of the token. In this case, we've hard-coded it to token #1. It is important to note that we're taking the assumption here that the extension will only be used for this token. When we call this function, we're saving the address of our core contract, and calling the mintExtensionNew function on it to mint the token.

The mint function is where we allow other people to mint more copies of this token. You can see that it is pretty simple, it prepares the input, and then calls mintExtensionExisting to mint another copy of an existing token (token #1 that we made in initialize).

The supportsInterface function simply tells other contracts that are calling this one what functions it supports.

The setBaseURI function lets us set the tokenURI we want to return. It also lets us update this information at any time in the future.

The tokenURI function returns this URI. It is important to note that this does not follow the EIP-1155 spec (as the extension does not keep track of tokens itself, it only helps mint them). The base contract, of course, has the uri function specified by the spec.

How to Deploy

1. Deploy core contract (using Manifold Studio is easiest) - example here

2. Deploy the extension contract - example here

3. Register the extension with #9 registerExtension on your base contract - example here

4. Initialize the extension with #2 initialize - example here

5. Set the baseURI for your extension - example here

6. Mint - example here

You should be able to see your token on OpenSea TestNet. Here is mine:

https://testnets.opensea.io/assets/0x9d5fb2d05ace6368b92723fd08b8572c6ddd1434/1

There are just a couple things to note here. The first is that this is token #1 on the core contract. Notice the OpenSea URL which has the address of the core contract. There are 2 tokens, and 2 owners. 1 of the tokens is owned by the wallet I called initialize with, and the other is owned by a wallet I called mint with.

FAQ

Is this contract an ERC1155 contract?

No - but it helps you mint tokens on an ERC1155 contract (your core contract)

Can this deployed contract be re-used?

Not in its current form. However, an extension can be written in such a way that it manages tokens for many different core contracts.

What is the gas cost for deploying an extension like this?

This particular extension cost me 1,833,652 gas to deploy. At gas prices of 40 gwei, that would be about 0.07 ETH.