ERC-721 Enumerable Transfer Facet

ERC-721 token transfers within a diamond

Key Features

• Exposes external functions for diamond routing of ERC-721 transfers.
• Accesses shared ERC-721 state via diamond storage.
• Supports standard ERC-721 transfer and safe transfer operations.
• Includes a mechanism (exportSelectors) for diamond selector discovery.

Overview

This facet implements ERC-721 token transfers as external functions in a diamond. It routes calls through the diamond proxy and accesses shared storage via ERC721Storage. Developers add this facet to expose token transfer functionality while maintaining upgradeability.

Storage

ERC721EnumerableStorage

Definition

struct ERC721EnumerableStorage {
  mapping(address owner => mapping(uint256 index => uint256 tokenId)) ownerTokens;
  mapping(uint256 tokenId => uint256 ownerTokensIndex) ownerTokensIndex;
  uint256[] allTokens;
  mapping(uint256 tokenId => uint256 allTokensIndex) allTokensIndex;
}

---

ERC721Storage

Definition

struct ERC721Storage {
  mapping(uint256 tokenId => address owner) ownerOf;
  mapping(address owner => uint256 balance) balanceOf;
  mapping(address owner => mapping(address operator => bool approved)) isApprovedForAll;
  mapping(uint256 tokenId => address approved) approved;
}

State Variables

Property	Type	Description
STORAGE_POSITION	bytes32	Diamond storage slot position for this module (Value: keccak256("erc721.enumerable"))
ERC721_STORAGE_POSITION	bytes32	Diamond storage slot position for this module (Value: keccak256("erc721"))

Functions

transferFrom

Transfers a token from one address to another.

function transferFrom(address _from, address _to, uint256 _tokenId) external;

Parameters:

Property	Type	Description
_from	address	The current owner of the token.
_to	address	The recipient address.
_tokenId	uint256	The token ID to transfer.

---

safeTransferFrom

Safely transfers a token, checking for receiver contract compatibility.

function safeTransferFrom(address _from, address _to, uint256 _tokenId) external;

Parameters:

Property	Type	Description
_from	address	The current owner of the token.
_to	address	The recipient address.
_tokenId	uint256	The token ID to transfer.

---

safeTransferFrom

Safely transfers a token with additional data.

function safeTransferFrom(address _from, address _to, uint256 _tokenId, bytes calldata _data) external;

Parameters:

Property	Type	Description
_from	address	The current owner of the token.
_to	address	The recipient address.
_tokenId	uint256	The token ID to transfer.
_data	bytes	Additional data to send to the receiver contract.

---

exportSelectors

Exports the function selectors of the ERC721EnumerableTransferFacet This function is use as a selector discovery mechanism for diamonds

function exportSelectors() external pure returns (bytes memory);

Returns:

Property	Type	Description
-	bytes	selectors The exported function selectors of the ERC721EnumerableTransferFacet

Events

Signature:

event Transfer(address indexed _from, address indexed _to, uint256 indexed _tokenId);

Errors

Signature:

error ERC721NonexistentToken(uint256 _tokenId);

Signature:

error ERC721IncorrectOwner(address _sender, uint256 _tokenId, address _owner);

Signature:

error ERC721InvalidReceiver(address _receiver);

Signature:

error ERC721InsufficientApproval(address _operator, uint256 _tokenId);

Best Practices

Best Practice

• Ensure the ERC721Storage struct is properly initialized and accessible by this facet.
• Verify that other facets do not interfere with the token ownership state managed by this facet.
• Call transferFrom, safeTransferFrom functions through the diamond proxy address.

Security Considerations

Security

The transferFrom and safeTransferFrom functions handle token ownership transfers. Reentrancy is mitigated by the checks-effects-interactions pattern. Input validation is crucial; ensure token IDs are valid and ownership rules are respected. Errors ERC721NonexistentToken, ERC721IncorrectOwner, ERC721InvalidReceiver, and ERC721InsufficientApproval are used to revert on invalid operations. The safeTransferFrom variations include checks for receiver contract compatibility.

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Last updated:March 13, 2026