Check out the accompanying article for the background.
The main file is ERC721C.sol. This is meant to be a shared contract among other client NFT contracts. Instead of bundling the 721 logic with the contract itself, the client NFT contracts call the already deployed ERC721C.
ERC721C is just an adapted version of OpenZeppelin's ERC-721 implementation. It was adapted in a way to make it shared.
🔴 This contract has not been thorougly tested so I don't recommend using it in production!!! 🔴
Examples are in the examples folder. There are 2 right now: CryptoCoven and InvisibleFriends.
Each example has 2 variants: The original implementation and the "C" variant (that uses ERC721C).
The tests folder has tests to measure gas of usage of deploying the original contracts compared to their "C" variant. It also has functions to measure mint, transfer. approve, and setApprovalForAll functions.
Here is a table of results:
Essentially ERC721C reduces deploy cost at the cost of transactions. This is not ideal, so it definitely needs improvement. See my article for my future plans.