ERC-721 Enumerable Mint Module

Mint ERC-721 tokens and manage enumeration lists

Key Features

• Internal functions for minting and enumeration management.
• Uses diamond storage pattern (EIP-8042) for shared state.
• Enforces ERC-721 token existence checks.
• Emits Transfer event upon successful minting.

Module Usage

This module provides internal functions for use in your custom facets. Import it to access shared logic and storage.

Overview

This module provides internal functions to mint ERC-721 tokens and maintain enumeration lists within a diamond. Facets can import this module to handle token creation and ensure that all minted tokens are tracked, making them accessible to other facets via shared diamond storage. This facilitates consistent state management across the diamond.

Storage

ERC721EnumerableStorage

storage-location: erc8042:erc721.enumerable

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

storage-location: erc8042:erc721

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

getERC721Storage

Returns a pointer to the ERC-721 storage struct. Uses inline assembly to access the storage slot defined by STORAGE_POSITION.

function getERC721Storage() pure returns (ERC721Storage storage s);

Returns:

Property	Type	Description
s	ERC721Storage	The ERC721Storage struct in storage.

---

getStorage

Returns the storage struct used by this facet.

function getStorage() pure returns (ERC721EnumerableStorage storage s);

Returns:

Property	Type	Description
s	ERC721EnumerableStorage	The ERC721Enumerable storage struct.

---

mint

Mints a new ERC-721 token to the specified address, adding it to enumeration lists. Reverts if the receiver address is zero or if the token already exists.

function mint(address _to, uint256 _tokenId) ;

Parameters:

Property	Type	Description
_to	address	The address that will own the newly minted token.
_tokenId	uint256	The ID of the token to mint.

Events

Emitted when a token is transferred between addresses.

Signature:

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

Errors

Thrown when the receiver address is invalid.

Signature:

error ERC721InvalidReceiver(address _receiver);

Thrown when the sender address is invalid.

Signature:

error ERC721InvalidSender(address _sender);

Best Practices

Best Practice

• Ensure the to address is not the zero address before calling mint.
• Verify that the tokenId does not already exist in storage to prevent re-minting.
• Call mint only after confirming necessary access controls are met by the calling facet.

Integration Notes

Shared Storage

This module interacts with diamond storage at the STORAGE_POSITION defined by keccak256(\"erc721.enumerable\"). The mint function reads from and writes to the ERC721EnumerableStorage struct, ensuring that newly minted tokens are added to internal enumeration lists. Changes to this storage are immediately visible to all facets operating on the same diamond storage layout.

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Last updated:March 13, 2026