set

set contract

The set contract can be found at contracts/set_nft.cairo.
Implementation is found in the contracts/set_nft/ folder.

High-level overview

The set contract is an augmented ERC 721. Unlike most ERC 721 collections, sets can be minted, burned and modified. The process of minting/burning is called assembling/disassembling.

Assembling/Disassembling a set

When minting a set, you pass a list of briqs to the assembly function. The set becomes the new owner of these tokens (essentially locking the tokens in the set). Inversely, when a set is disassembled/burned, the briqs are transferred back to the set owner.

Note that for gas-efficiency, the full list of briqs is expected during assembly and disassembly.

Set token ID & token URI

Token ID

The set token_id is crafted very specifically. The requirements are:

• The token_id should not conflict with any wallet address, or the set would become owner of the wallet's briqs (and vice-versa).
• The token_id should be computable before the minting transaction is complete (for convenience).

To enforce these contraints, the set token_id must not be chosable, but nonetheless predictable. The approach taken consists of on-chain hashing the wallet address & a 'hint' into the token_id. The top 192 bits are kept. Assuming pedersen_hashing is cryptographically secure, we avoid attackers creating sets with the same token_id as a wallet (a fortiori a specific wallet), while remaining predictable.

token URI

The set token URI is generally stored in its own storage_var. However, if the token URI is small enough (less than 310 bits total), we store part of it in the token ID, using the bits left free (see above, the token_id only uses 192 bits). The token ID is then frozen in place (further changes to the token URI will ignore the bit in the token ID).

Instead of storing the total length, the token URI uses the top bits of a felt (248/249/250) to store whether the token URI continues.

API

In general, there are two versions of each view/external functions:

• One taking felt arguments, that end with an extra _.
• One taking Uint256 arguments, that don't.

The default interface takes Uint256 for compatibility with the OpenZeppelin contracts, which are expected to become standard on Cairo. However, since sets are Cairo-native, the set contract uses felt internally for efficiency.

Balance

The usual ERC 721 functions are provided: balanceOf, ownerOf, along with tokenOfOwnerByIndex & balanceDetailsOf to get the full list.

Transfer

Only transferFrom is currently implemented.