63 lines
2.7 KiB
Markdown
63 lines
2.7 KiB
Markdown
---
|
|
eip: 4521
|
|
title: 721/20-compatible transfer
|
|
description: Recommends a simple extension to make NFTs compatible with apps and contracts that handle fungibles.
|
|
author: Ross Campbell (@z0r0z)
|
|
discussions-to: https://ethereum-magicians.org/t/eip-4521-721-20-compatible-transfer/7903
|
|
status: Stagnant
|
|
type: Standards Track
|
|
category: ERC
|
|
created: 2021-12-13
|
|
requires: 721
|
|
---
|
|
|
|
## Abstract
|
|
ERC-721, the popular standard for non-fungible tokens (NFTs), includes send functions, such as `transferFrom()` and `safeTransferFrom()`, but does not include a backwards-compatible `transfer()` found in fungible ERC-20 tokens. This standard provides references to add such a `transfer()`.
|
|
|
|
## Motivation
|
|
This standard proposes a simple extension to allow NFTs to work with contracts designed to manage ERC-20s and many consumer wallets which expect to be able to execute a token `transfer()`. For example, if an NFT is inadvertently sent to a contract that typically handles ERC-20, that NFT will be locked. It should also simplify the task for contract programmers if they can rely on `transfer()` to both handle ERC-20 and NFTs.
|
|
|
|
## Specification
|
|
The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in RFC 2119.
|
|
|
|
The interface for ERC-4521 `transfer()` MUST conform to ERC-20 and resulting transfers MUST fire the `Transfer` event as described in ERC-721.
|
|
|
|
```sol
|
|
function transfer(address to, uint256 tokenId) external returns (bool success);
|
|
```
|
|
|
|
## Rationale
|
|
Replicating ERC-20 `transfer()` with just a minor change to accurately reflect that a unique `tokenId` rather than fungible sum is being sent is desirable for code simplicity and to make integration easier.
|
|
|
|
## Backwards Compatibility
|
|
This EIP does not introduce any known backward compatibility issues.
|
|
|
|
## Reference Implementation
|
|
A reference implementation of an ERC-4521 `transfer()`:
|
|
|
|
```sol
|
|
function transfer(address to, uint256 tokenId) public virtual returns (bool success) {
|
|
require(msg.sender == ownerOf[tokenId], "NOT_OWNER");
|
|
|
|
unchecked {
|
|
balanceOf[msg.sender]--;
|
|
|
|
balanceOf[to]++;
|
|
}
|
|
|
|
delete getApproved[tokenId];
|
|
|
|
ownerOf[tokenId] = to;
|
|
|
|
emit Transfer(msg.sender, to, tokenId);
|
|
|
|
success = true;
|
|
}
|
|
```
|
|
|
|
## Security Considerations
|
|
Implementers must be sure to include the relevant return `bool` value for an ERC-4521 in order to conform with existing contracts that use ERC-20 interfaces, otherwise, NFTs may be locked unless a `safeTransfer` is used in such contracts.
|
|
|
|
## Copyright
|
|
Copyright and related rights waived via [CC0](../LICENSE.md).
|