ERC-721 Approve Module

Manages ERC-721 token approvals and operator status

Key Features

• Provides internal functions for ERC-721 token approvals and operator management.
• Utilizes the diamond storage pattern (EIP-8042) for shared state.
• No external dependencies, promoting composability within a diamond.
• Emits Approval and ApprovalForAll events upon successful state changes.

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 for managing ERC-721 token approvals and operator status within a diamond. Facets can import this module to interact with shared ERC-721 storage, ensuring consistent state management across the diamond. Changes to approvals and operator statuses are immediately visible to all facets accessing the same diamond storage.

Storage

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"))

Functions

approve

Approves another address to transfer the given token ID.

function approve(address _to, uint256 _tokenId) ;

Parameters:

Property	Type	Description
_to	address	The address to be approved.
_tokenId	uint256	The token ID to approve.

---

getStorage

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

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

Returns:

Property	Type	Description
s	ERC721Storage	The ERC721Storage struct in storage.

---

setApprovalForAll

Approves or revokes permission for an operator to manage all users's assets.

function setApprovalForAll(address user, address _operator, bool _approved) ;

Parameters:

Property	Type	Description
_operator	address	The operator address to set approval for.
_approved	bool	True to approve, false to revoke.

Events

Emitted when the approved address for an NFT is changed or reaffirmed.

Signature:

event Approval(address indexed _owner, address indexed _to, uint256 indexed _tokenId);

Emitted when an operator is enabled or disabled for an owner.

Signature:

event ApprovalForAll(address indexed _owner, address indexed _operator, bool _approved);

Errors

Error indicating the operator address is invalid.

Signature:

error ERC721InvalidOperator(address _operator);

Title: ERC-721 Approve Module Error indicating that the queried token does not exist.

Signature:

error ERC721NonexistentToken(uint256 _tokenId);

Best Practices

Best Practice

• Call approve or setApprovalForAll only after verifying caller permissions if required by your facet's logic.
• Ensure the ERC721Storage struct definition in your facet matches the one defined in this module to prevent storage collisions.
• Handle potential errors like ERC721NonexistentToken or ERC721InvalidOperator when calling the module's functions.

Integration Notes

Shared Storage

This module interacts with diamond storage at the slot identified by STORAGE_POSITION, which is defined as keccak256(\"erc721\"). It uses the ERC721Storage struct to manage approval data. All state modifications made through this module are written directly to this shared storage slot, making them immediately visible to any other facet within the same diamond that reads from or writes to this storage position.

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Last updated:March 13, 2026