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Micro ERC721

This contains my WIP experiments creating a smaller footprint ERC721.

TODO package/publish for use, doc install

SizedERC721 - size-optimized ERC721

This is a drop-in replacement for the OpenZeppelin ERC721 that uses storage optimizations for a specified maximum size. This lets it keep gas costs low for mint/transfer/burn while also adding extra functionality (e.g. IERC721Enumerable-tokenOfOwnerByIndex).

Whereas ERC721 supports any uint256 ID and up to 2^256 tokens, this SizedERC721 requires a specified maximum token ID (e.g. 10,000) and token IDs can then only be minted within that range (e.g. 0 - 10,000). This is a typical assumption many projects enforce anyways.

Benchmarks

  • ExampleSized runs are instances of SizedERC721.
  • OZVanilla runs are instances of OpenZeppelin's ERC721.
  • OZEnumerable runs are instances of OpenZeppelin's ERC721Enumerable.
  • ChiruERC721 runs are instances of Chiru Lab's ERC721a.

Right now the SizedERC721 has the same gas prices as OpenZeppelin's vanilla ERC721 for mint/burn/transfer. But it does this while also implementing IERC721Enumerable-tokenOfOwnerByIndex. By contrast, the OpenZeppelin edition of ERC721Enumerable (which includes tokenOfOwnerByIndex) dramatically increases the mint/burn/transfers costs by 2x-3x. So this means your SizedERC721 can list a person's tokens on-chain w/o a big spike in the cost of a mint.

Multi-minting

Chiru Lab's ERC721a does some clever stuff to make multi-minting (minting more than one at a time) cheaper up-front. It offloads some of those minting costs on later transfers and requires tokens mint use sequential IDs starting from 0.

I've added multiMinting to the benchmark to track this. Comparing multi-minting costs is a little tricky. Where Chiru is a hair costlier for n = 1 it quickly becomes the cheapest for minting multiple. And if you look at transferFrom, you can see where it offloads that onto later transfers.

benchmark of micro ERC721

TODO doc data structure cleverness / next explorations

  • TODO explain EnumerableBitMaps
  • TODO explore incorporating Chiru's null-run technique for SizedERC721's _owners (and/or consider contributing to ERC721a to speed up enumeration)
  • TODO explore static indexed 8192 (8x32 index (fits into 1 uint256) for a 8x256 bitmap of holdings)

development setup

  • $ npm install
  • $ npm test
  • $ npm run pretty
  • $ REPORT_GAS=true npm test