Gas Usage Reduction 🏗⛽

With the smart contract deployed here as a baseline, this document describes a number of modifications, implemented by the smart contract in this GitHub repository.

Storage

The optimizations described in the following section realize performance improvements by enhancing the way that data is allocated.

_IPFSHashHasBeenSet

The _IPFSHashHasBeenSet mapping indicates whether a niftyType has been allocated an IPFS hash.

mapping (uint => bool) public _IPFSHashHasBeenSet;`

The mapping can be made redundant by setting _niftyIPFSHashes[niftyType] to a default value which indicates that it hasn't yet been assigned, e.g. 0000000000000000000000000000000000000000000000. Resulting in the following:

function setNiftyIPFSHash(uint niftyType, string memory ipfs_hash) onlyValidSender public {    
    require(_niftyIPFSHashes[niftyType] != "0000000000000000000000000000000000000000000000", "Can only be set once.");
    _niftyIPFSHashes[niftyType] = ipfs_hash;
}

Allowing us to safely remove the _IPFSHashHasBeenSet mapping. As an aside, additional gas savings can be achieved by removing the error message from the require() statement.

_niftyIPFSHashes

The function _setTokenIPFSHash from ERC721Metadata is biased to 1/1 tokens.

_setTokenIPFSHash(tokenId, ipfsHash);

For nifties such as The OG (n/50) we end up with the following:

{"6200050001":"QmdKektfKmAEw7f692D7G5yQbacQomeaRmgMDnpqG9bcJv",
 "6200050002":"QmdKektfKmAEw7f692D7G5yQbacQomeaRmgMDnpqG9bcJv",
 "6200050050":"QmdKektfKmAEw7f692D7G5yQbacQomeaRmgMDnpqG9bcJv"}

Since the association of an edition with an IPFS hash is likewise stored in _niftyIPFSHashes[niftyType] we could, without loss of generality, set this ERC721Metadata property with the niftyType exclusively, or without reference to the specificTokenId like so:

{"62000500":"QmdKektfKmAEw7f692D7G5yQbacQomeaRmgMDnpqG9bcJv"}

As the metadata extension is considered optional for ERC721 compliance the call to _setTokenIPFSHash(tokenId, ipfsHash) could be removed entirely.

Execution

Assembly

Requires more testing, could be optimized away by the compiler but...

Batch minting

Possibility of out fo gas errors...

Design

This section comprises possible simplifications of the design patterns used with an eye toward efficiency and comprehensibility.

isNiftySoldOut × niftyType

The prompt mentions that a nifty type "gives no information about the edition size", which mean the following check could be removed:

function isNiftySoldOut(uint niftyType) public view returns (bool) {
    if (niftyType > numNiftiesCurrentlyInContract) {...}
}

The new isNiftySoldOut() method body would look like so:

if (_numNiftyMinted[niftyType].current() > _numNiftyPermitted[niftyType]) {
    return (true);
}
return (false);

Inheritance

There are two instances of the niftyRegistryContract address, once in BuilderShop and once in NiftyBuilderInstance.

contract NiftyCore {
   address public addressRegistry = 0x6e53130dDfF21E3BC963Ee902005223b9A202106;
}

The value could be abstracted into a super class, providing for more efficient and less resource intensive architecture.